2019-05-27 14:55:01 +08:00
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// SPDX-License-Identifier: GPL-2.0-or-later
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2015-06-01 19:43:56 +08:00
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/*
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crypto: chacha - add XChaCha12 support
Now that the generic implementation of ChaCha20 has been refactored to
allow varying the number of rounds, add support for XChaCha12, which is
the XSalsa construction applied to ChaCha12. ChaCha12 is one of the
three ciphers specified by the original ChaCha paper
(https://cr.yp.to/chacha/chacha-20080128.pdf: "ChaCha, a variant of
Salsa20"), alongside ChaCha8 and ChaCha20. ChaCha12 is faster than
ChaCha20 but has a lower, but still large, security margin.
We need XChaCha12 support so that it can be used in the Adiantum
encryption mode, which enables disk/file encryption on low-end mobile
devices where AES-XTS is too slow as the CPUs lack AES instructions.
We'd prefer XChaCha20 (the more popular variant), but it's too slow on
some of our target devices, so at least in some cases we do need the
XChaCha12-based version. In more detail, the problem is that Adiantum
is still much slower than we're happy with, and encryption still has a
quite noticeable effect on the feel of low-end devices. Users and
vendors push back hard against encryption that degrades the user
experience, which always risks encryption being disabled entirely. So
we need to choose the fastest option that gives us a solid margin of
security, and here that's XChaCha12. The best known attack on ChaCha
breaks only 7 rounds and has 2^235 time complexity, so ChaCha12's
security margin is still better than AES-256's. Much has been learned
about cryptanalysis of ARX ciphers since Salsa20 was originally designed
in 2005, and it now seems we can be comfortable with a smaller number of
rounds. The eSTREAM project also suggests the 12-round version of
Salsa20 as providing the best balance among the different variants:
combining very good performance with a "comfortable margin of security".
Note that it would be trivial to add vanilla ChaCha12 in addition to
XChaCha12. However, it's unneeded for now and therefore is omitted.
As discussed in the patch that introduced XChaCha20 support, I
considered splitting the code into separate chacha-common, chacha20,
xchacha20, and xchacha12 modules, so that these algorithms could be
enabled/disabled independently. However, since nearly all the code is
shared anyway, I ultimately decided there would have been little benefit
to the added complexity.
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Martin Willi <martin@strongswan.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2018-11-17 09:26:22 +08:00
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* ChaCha and XChaCha stream ciphers, including ChaCha20 (RFC7539)
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2015-06-01 19:43:56 +08:00
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*
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* Copyright (C) 2015 Martin Willi
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crypto: chacha20-generic - add XChaCha20 support
Add support for the XChaCha20 stream cipher. XChaCha20 is the
application of the XSalsa20 construction
(https://cr.yp.to/snuffle/xsalsa-20081128.pdf) to ChaCha20 rather than
to Salsa20. XChaCha20 extends ChaCha20's nonce length from 64 bits (or
96 bits, depending on convention) to 192 bits, while provably retaining
ChaCha20's security. XChaCha20 uses the ChaCha20 permutation to map the
key and first 128 nonce bits to a 256-bit subkey. Then, it does the
ChaCha20 stream cipher with the subkey and remaining 64 bits of nonce.
We need XChaCha support in order to add support for the Adiantum
encryption mode. Note that to meet our performance requirements, we
actually plan to primarily use the variant XChaCha12. But we believe
it's wise to first add XChaCha20 as a baseline with a higher security
margin, in case there are any situations where it can be used.
Supporting both variants is straightforward.
Since XChaCha20's subkey differs for each request, XChaCha20 can't be a
template that wraps ChaCha20; that would require re-keying the
underlying ChaCha20 for every request, which wouldn't be thread-safe.
Instead, we make XChaCha20 its own top-level algorithm which calls the
ChaCha20 streaming implementation internally.
Similar to the existing ChaCha20 implementation, we define the IV to be
the nonce and stream position concatenated together. This allows users
to seek to any position in the stream.
I considered splitting the code into separate chacha20-common, chacha20,
and xchacha20 modules, so that chacha20 and xchacha20 could be
enabled/disabled independently. However, since nearly all the code is
shared anyway, I ultimately decided there would have been little benefit
to the added complexity of separate modules.
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Martin Willi <martin@strongswan.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2018-11-17 09:26:20 +08:00
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* Copyright (C) 2018 Google LLC
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2015-06-01 19:43:56 +08:00
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*/
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2017-11-23 03:51:36 +08:00
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#include <asm/unaligned.h>
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2015-06-01 19:43:56 +08:00
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#include <crypto/algapi.h>
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2019-11-08 20:22:08 +08:00
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#include <crypto/internal/chacha.h>
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2016-12-09 22:33:51 +08:00
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#include <crypto/internal/skcipher.h>
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#include <linux/module.h>
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2015-06-01 19:43:56 +08:00
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2018-11-17 09:26:21 +08:00
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static int chacha_stream_xor(struct skcipher_request *req,
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2019-06-03 13:47:14 +08:00
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const struct chacha_ctx *ctx, const u8 *iv)
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crypto: chacha20-generic - add XChaCha20 support
Add support for the XChaCha20 stream cipher. XChaCha20 is the
application of the XSalsa20 construction
(https://cr.yp.to/snuffle/xsalsa-20081128.pdf) to ChaCha20 rather than
to Salsa20. XChaCha20 extends ChaCha20's nonce length from 64 bits (or
96 bits, depending on convention) to 192 bits, while provably retaining
ChaCha20's security. XChaCha20 uses the ChaCha20 permutation to map the
key and first 128 nonce bits to a 256-bit subkey. Then, it does the
ChaCha20 stream cipher with the subkey and remaining 64 bits of nonce.
We need XChaCha support in order to add support for the Adiantum
encryption mode. Note that to meet our performance requirements, we
actually plan to primarily use the variant XChaCha12. But we believe
it's wise to first add XChaCha20 as a baseline with a higher security
margin, in case there are any situations where it can be used.
Supporting both variants is straightforward.
Since XChaCha20's subkey differs for each request, XChaCha20 can't be a
template that wraps ChaCha20; that would require re-keying the
underlying ChaCha20 for every request, which wouldn't be thread-safe.
Instead, we make XChaCha20 its own top-level algorithm which calls the
ChaCha20 streaming implementation internally.
Similar to the existing ChaCha20 implementation, we define the IV to be
the nonce and stream position concatenated together. This allows users
to seek to any position in the stream.
I considered splitting the code into separate chacha20-common, chacha20,
and xchacha20 modules, so that chacha20 and xchacha20 could be
enabled/disabled independently. However, since nearly all the code is
shared anyway, I ultimately decided there would have been little benefit
to the added complexity of separate modules.
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Martin Willi <martin@strongswan.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2018-11-17 09:26:20 +08:00
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{
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struct skcipher_walk walk;
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u32 state[16];
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int err;
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err = skcipher_walk_virt(&walk, req, false);
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2019-11-08 20:22:18 +08:00
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chacha_init_generic(state, ctx->key, iv);
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crypto: chacha20-generic - add XChaCha20 support
Add support for the XChaCha20 stream cipher. XChaCha20 is the
application of the XSalsa20 construction
(https://cr.yp.to/snuffle/xsalsa-20081128.pdf) to ChaCha20 rather than
to Salsa20. XChaCha20 extends ChaCha20's nonce length from 64 bits (or
96 bits, depending on convention) to 192 bits, while provably retaining
ChaCha20's security. XChaCha20 uses the ChaCha20 permutation to map the
key and first 128 nonce bits to a 256-bit subkey. Then, it does the
ChaCha20 stream cipher with the subkey and remaining 64 bits of nonce.
We need XChaCha support in order to add support for the Adiantum
encryption mode. Note that to meet our performance requirements, we
actually plan to primarily use the variant XChaCha12. But we believe
it's wise to first add XChaCha20 as a baseline with a higher security
margin, in case there are any situations where it can be used.
Supporting both variants is straightforward.
Since XChaCha20's subkey differs for each request, XChaCha20 can't be a
template that wraps ChaCha20; that would require re-keying the
underlying ChaCha20 for every request, which wouldn't be thread-safe.
Instead, we make XChaCha20 its own top-level algorithm which calls the
ChaCha20 streaming implementation internally.
Similar to the existing ChaCha20 implementation, we define the IV to be
the nonce and stream position concatenated together. This allows users
to seek to any position in the stream.
I considered splitting the code into separate chacha20-common, chacha20,
and xchacha20 modules, so that chacha20 and xchacha20 could be
enabled/disabled independently. However, since nearly all the code is
shared anyway, I ultimately decided there would have been little benefit
to the added complexity of separate modules.
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Martin Willi <martin@strongswan.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2018-11-17 09:26:20 +08:00
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while (walk.nbytes > 0) {
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unsigned int nbytes = walk.nbytes;
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if (nbytes < walk.total)
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crypto: chacha-generic - fix use as arm64 no-NEON fallback
The arm64 implementations of ChaCha and XChaCha are failing the extra
crypto self-tests following my patches to test the !may_use_simd() code
paths, which previously were untested. The problem is as follows:
When !may_use_simd(), the arm64 NEON implementations fall back to the
generic implementation, which uses the skcipher_walk API to iterate
through the src/dst scatterlists. Due to how the skcipher_walk API
works, walk.stride is set from the skcipher_alg actually being used,
which in this case is the arm64 NEON algorithm. Thus walk.stride is
5*CHACHA_BLOCK_SIZE, not CHACHA_BLOCK_SIZE.
This unnecessarily large stride shouldn't cause an actual problem.
However, the generic implementation computes round_down(nbytes,
walk.stride). round_down() assumes the round amount is a power of 2,
which 5*CHACHA_BLOCK_SIZE is not, so it gives the wrong result.
This causes the following case in skcipher_walk_done() to be hit,
causing a WARN() and failing the encryption operation:
if (WARN_ON(err)) {
/* unexpected case; didn't process all bytes */
err = -EINVAL;
goto finish;
}
Fix it by rounding down to CHACHA_BLOCK_SIZE instead of walk.stride.
(Or we could replace round_down() with rounddown(), but that would add a
slow division operation every time, which I think we should avoid.)
Fixes: 2fe55987b262 ("crypto: arm64/chacha - use combined SIMD/ALU routine for more speed")
Cc: <stable@vger.kernel.org> # v5.0+
Signed-off-by: Eric Biggers <ebiggers@google.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2019-03-13 13:12:45 +08:00
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nbytes = round_down(nbytes, CHACHA_BLOCK_SIZE);
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crypto: chacha20-generic - add XChaCha20 support
Add support for the XChaCha20 stream cipher. XChaCha20 is the
application of the XSalsa20 construction
(https://cr.yp.to/snuffle/xsalsa-20081128.pdf) to ChaCha20 rather than
to Salsa20. XChaCha20 extends ChaCha20's nonce length from 64 bits (or
96 bits, depending on convention) to 192 bits, while provably retaining
ChaCha20's security. XChaCha20 uses the ChaCha20 permutation to map the
key and first 128 nonce bits to a 256-bit subkey. Then, it does the
ChaCha20 stream cipher with the subkey and remaining 64 bits of nonce.
We need XChaCha support in order to add support for the Adiantum
encryption mode. Note that to meet our performance requirements, we
actually plan to primarily use the variant XChaCha12. But we believe
it's wise to first add XChaCha20 as a baseline with a higher security
margin, in case there are any situations where it can be used.
Supporting both variants is straightforward.
Since XChaCha20's subkey differs for each request, XChaCha20 can't be a
template that wraps ChaCha20; that would require re-keying the
underlying ChaCha20 for every request, which wouldn't be thread-safe.
Instead, we make XChaCha20 its own top-level algorithm which calls the
ChaCha20 streaming implementation internally.
Similar to the existing ChaCha20 implementation, we define the IV to be
the nonce and stream position concatenated together. This allows users
to seek to any position in the stream.
I considered splitting the code into separate chacha20-common, chacha20,
and xchacha20 modules, so that chacha20 and xchacha20 could be
enabled/disabled independently. However, since nearly all the code is
shared anyway, I ultimately decided there would have been little benefit
to the added complexity of separate modules.
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Martin Willi <martin@strongswan.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2018-11-17 09:26:20 +08:00
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2019-11-08 20:22:08 +08:00
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chacha_crypt_generic(state, walk.dst.virt.addr,
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walk.src.virt.addr, nbytes, ctx->nrounds);
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crypto: chacha20-generic - add XChaCha20 support
Add support for the XChaCha20 stream cipher. XChaCha20 is the
application of the XSalsa20 construction
(https://cr.yp.to/snuffle/xsalsa-20081128.pdf) to ChaCha20 rather than
to Salsa20. XChaCha20 extends ChaCha20's nonce length from 64 bits (or
96 bits, depending on convention) to 192 bits, while provably retaining
ChaCha20's security. XChaCha20 uses the ChaCha20 permutation to map the
key and first 128 nonce bits to a 256-bit subkey. Then, it does the
ChaCha20 stream cipher with the subkey and remaining 64 bits of nonce.
We need XChaCha support in order to add support for the Adiantum
encryption mode. Note that to meet our performance requirements, we
actually plan to primarily use the variant XChaCha12. But we believe
it's wise to first add XChaCha20 as a baseline with a higher security
margin, in case there are any situations where it can be used.
Supporting both variants is straightforward.
Since XChaCha20's subkey differs for each request, XChaCha20 can't be a
template that wraps ChaCha20; that would require re-keying the
underlying ChaCha20 for every request, which wouldn't be thread-safe.
Instead, we make XChaCha20 its own top-level algorithm which calls the
ChaCha20 streaming implementation internally.
Similar to the existing ChaCha20 implementation, we define the IV to be
the nonce and stream position concatenated together. This allows users
to seek to any position in the stream.
I considered splitting the code into separate chacha20-common, chacha20,
and xchacha20 modules, so that chacha20 and xchacha20 could be
enabled/disabled independently. However, since nearly all the code is
shared anyway, I ultimately decided there would have been little benefit
to the added complexity of separate modules.
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Martin Willi <martin@strongswan.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2018-11-17 09:26:20 +08:00
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err = skcipher_walk_done(&walk, walk.nbytes - nbytes);
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}
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return err;
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}
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2019-11-08 20:22:18 +08:00
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static int crypto_chacha_crypt(struct skcipher_request *req)
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2015-06-01 19:43:56 +08:00
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{
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2016-12-09 22:33:51 +08:00
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struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
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2018-11-17 09:26:21 +08:00
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struct chacha_ctx *ctx = crypto_skcipher_ctx(tfm);
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2015-06-01 19:43:56 +08:00
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2018-11-17 09:26:21 +08:00
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return chacha_stream_xor(req, ctx, req->iv);
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crypto: chacha20-generic - add XChaCha20 support
Add support for the XChaCha20 stream cipher. XChaCha20 is the
application of the XSalsa20 construction
(https://cr.yp.to/snuffle/xsalsa-20081128.pdf) to ChaCha20 rather than
to Salsa20. XChaCha20 extends ChaCha20's nonce length from 64 bits (or
96 bits, depending on convention) to 192 bits, while provably retaining
ChaCha20's security. XChaCha20 uses the ChaCha20 permutation to map the
key and first 128 nonce bits to a 256-bit subkey. Then, it does the
ChaCha20 stream cipher with the subkey and remaining 64 bits of nonce.
We need XChaCha support in order to add support for the Adiantum
encryption mode. Note that to meet our performance requirements, we
actually plan to primarily use the variant XChaCha12. But we believe
it's wise to first add XChaCha20 as a baseline with a higher security
margin, in case there are any situations where it can be used.
Supporting both variants is straightforward.
Since XChaCha20's subkey differs for each request, XChaCha20 can't be a
template that wraps ChaCha20; that would require re-keying the
underlying ChaCha20 for every request, which wouldn't be thread-safe.
Instead, we make XChaCha20 its own top-level algorithm which calls the
ChaCha20 streaming implementation internally.
Similar to the existing ChaCha20 implementation, we define the IV to be
the nonce and stream position concatenated together. This allows users
to seek to any position in the stream.
I considered splitting the code into separate chacha20-common, chacha20,
and xchacha20 modules, so that chacha20 and xchacha20 could be
enabled/disabled independently. However, since nearly all the code is
shared anyway, I ultimately decided there would have been little benefit
to the added complexity of separate modules.
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Martin Willi <martin@strongswan.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2018-11-17 09:26:20 +08:00
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}
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2015-06-01 19:43:56 +08:00
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2019-11-08 20:22:18 +08:00
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static int crypto_xchacha_crypt(struct skcipher_request *req)
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crypto: chacha20-generic - add XChaCha20 support
Add support for the XChaCha20 stream cipher. XChaCha20 is the
application of the XSalsa20 construction
(https://cr.yp.to/snuffle/xsalsa-20081128.pdf) to ChaCha20 rather than
to Salsa20. XChaCha20 extends ChaCha20's nonce length from 64 bits (or
96 bits, depending on convention) to 192 bits, while provably retaining
ChaCha20's security. XChaCha20 uses the ChaCha20 permutation to map the
key and first 128 nonce bits to a 256-bit subkey. Then, it does the
ChaCha20 stream cipher with the subkey and remaining 64 bits of nonce.
We need XChaCha support in order to add support for the Adiantum
encryption mode. Note that to meet our performance requirements, we
actually plan to primarily use the variant XChaCha12. But we believe
it's wise to first add XChaCha20 as a baseline with a higher security
margin, in case there are any situations where it can be used.
Supporting both variants is straightforward.
Since XChaCha20's subkey differs for each request, XChaCha20 can't be a
template that wraps ChaCha20; that would require re-keying the
underlying ChaCha20 for every request, which wouldn't be thread-safe.
Instead, we make XChaCha20 its own top-level algorithm which calls the
ChaCha20 streaming implementation internally.
Similar to the existing ChaCha20 implementation, we define the IV to be
the nonce and stream position concatenated together. This allows users
to seek to any position in the stream.
I considered splitting the code into separate chacha20-common, chacha20,
and xchacha20 modules, so that chacha20 and xchacha20 could be
enabled/disabled independently. However, since nearly all the code is
shared anyway, I ultimately decided there would have been little benefit
to the added complexity of separate modules.
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Martin Willi <martin@strongswan.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2018-11-17 09:26:20 +08:00
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{
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struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
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2018-11-17 09:26:21 +08:00
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struct chacha_ctx *ctx = crypto_skcipher_ctx(tfm);
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struct chacha_ctx subctx;
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crypto: chacha20-generic - add XChaCha20 support
Add support for the XChaCha20 stream cipher. XChaCha20 is the
application of the XSalsa20 construction
(https://cr.yp.to/snuffle/xsalsa-20081128.pdf) to ChaCha20 rather than
to Salsa20. XChaCha20 extends ChaCha20's nonce length from 64 bits (or
96 bits, depending on convention) to 192 bits, while provably retaining
ChaCha20's security. XChaCha20 uses the ChaCha20 permutation to map the
key and first 128 nonce bits to a 256-bit subkey. Then, it does the
ChaCha20 stream cipher with the subkey and remaining 64 bits of nonce.
We need XChaCha support in order to add support for the Adiantum
encryption mode. Note that to meet our performance requirements, we
actually plan to primarily use the variant XChaCha12. But we believe
it's wise to first add XChaCha20 as a baseline with a higher security
margin, in case there are any situations where it can be used.
Supporting both variants is straightforward.
Since XChaCha20's subkey differs for each request, XChaCha20 can't be a
template that wraps ChaCha20; that would require re-keying the
underlying ChaCha20 for every request, which wouldn't be thread-safe.
Instead, we make XChaCha20 its own top-level algorithm which calls the
ChaCha20 streaming implementation internally.
Similar to the existing ChaCha20 implementation, we define the IV to be
the nonce and stream position concatenated together. This allows users
to seek to any position in the stream.
I considered splitting the code into separate chacha20-common, chacha20,
and xchacha20 modules, so that chacha20 and xchacha20 could be
enabled/disabled independently. However, since nearly all the code is
shared anyway, I ultimately decided there would have been little benefit
to the added complexity of separate modules.
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Martin Willi <martin@strongswan.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2018-11-17 09:26:20 +08:00
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u32 state[16];
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u8 real_iv[16];
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2017-08-14 21:28:14 +08:00
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crypto: chacha20-generic - add XChaCha20 support
Add support for the XChaCha20 stream cipher. XChaCha20 is the
application of the XSalsa20 construction
(https://cr.yp.to/snuffle/xsalsa-20081128.pdf) to ChaCha20 rather than
to Salsa20. XChaCha20 extends ChaCha20's nonce length from 64 bits (or
96 bits, depending on convention) to 192 bits, while provably retaining
ChaCha20's security. XChaCha20 uses the ChaCha20 permutation to map the
key and first 128 nonce bits to a 256-bit subkey. Then, it does the
ChaCha20 stream cipher with the subkey and remaining 64 bits of nonce.
We need XChaCha support in order to add support for the Adiantum
encryption mode. Note that to meet our performance requirements, we
actually plan to primarily use the variant XChaCha12. But we believe
it's wise to first add XChaCha20 as a baseline with a higher security
margin, in case there are any situations where it can be used.
Supporting both variants is straightforward.
Since XChaCha20's subkey differs for each request, XChaCha20 can't be a
template that wraps ChaCha20; that would require re-keying the
underlying ChaCha20 for every request, which wouldn't be thread-safe.
Instead, we make XChaCha20 its own top-level algorithm which calls the
ChaCha20 streaming implementation internally.
Similar to the existing ChaCha20 implementation, we define the IV to be
the nonce and stream position concatenated together. This allows users
to seek to any position in the stream.
I considered splitting the code into separate chacha20-common, chacha20,
and xchacha20 modules, so that chacha20 and xchacha20 could be
enabled/disabled independently. However, since nearly all the code is
shared anyway, I ultimately decided there would have been little benefit
to the added complexity of separate modules.
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Martin Willi <martin@strongswan.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2018-11-17 09:26:20 +08:00
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|
|
/* Compute the subkey given the original key and first 128 nonce bits */
|
2019-11-08 20:22:18 +08:00
|
|
|
chacha_init_generic(state, ctx->key, req->iv);
|
2019-11-08 20:22:08 +08:00
|
|
|
hchacha_block_generic(state, subctx.key, ctx->nrounds);
|
2018-11-17 09:26:21 +08:00
|
|
|
subctx.nrounds = ctx->nrounds;
|
2017-08-14 21:28:14 +08:00
|
|
|
|
crypto: chacha20-generic - add XChaCha20 support
Add support for the XChaCha20 stream cipher. XChaCha20 is the
application of the XSalsa20 construction
(https://cr.yp.to/snuffle/xsalsa-20081128.pdf) to ChaCha20 rather than
to Salsa20. XChaCha20 extends ChaCha20's nonce length from 64 bits (or
96 bits, depending on convention) to 192 bits, while provably retaining
ChaCha20's security. XChaCha20 uses the ChaCha20 permutation to map the
key and first 128 nonce bits to a 256-bit subkey. Then, it does the
ChaCha20 stream cipher with the subkey and remaining 64 bits of nonce.
We need XChaCha support in order to add support for the Adiantum
encryption mode. Note that to meet our performance requirements, we
actually plan to primarily use the variant XChaCha12. But we believe
it's wise to first add XChaCha20 as a baseline with a higher security
margin, in case there are any situations where it can be used.
Supporting both variants is straightforward.
Since XChaCha20's subkey differs for each request, XChaCha20 can't be a
template that wraps ChaCha20; that would require re-keying the
underlying ChaCha20 for every request, which wouldn't be thread-safe.
Instead, we make XChaCha20 its own top-level algorithm which calls the
ChaCha20 streaming implementation internally.
Similar to the existing ChaCha20 implementation, we define the IV to be
the nonce and stream position concatenated together. This allows users
to seek to any position in the stream.
I considered splitting the code into separate chacha20-common, chacha20,
and xchacha20 modules, so that chacha20 and xchacha20 could be
enabled/disabled independently. However, since nearly all the code is
shared anyway, I ultimately decided there would have been little benefit
to the added complexity of separate modules.
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Martin Willi <martin@strongswan.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2018-11-17 09:26:20 +08:00
|
|
|
/* Build the real IV */
|
|
|
|
|
memcpy(&real_iv[0], req->iv + 24, 8); /* stream position */
|
|
|
|
|
memcpy(&real_iv[8], req->iv + 16, 8); /* remaining 64 nonce bits */
|
2015-06-01 19:43:56 +08:00
|
|
|
|
crypto: chacha20-generic - add XChaCha20 support
Add support for the XChaCha20 stream cipher. XChaCha20 is the
application of the XSalsa20 construction
(https://cr.yp.to/snuffle/xsalsa-20081128.pdf) to ChaCha20 rather than
to Salsa20. XChaCha20 extends ChaCha20's nonce length from 64 bits (or
96 bits, depending on convention) to 192 bits, while provably retaining
ChaCha20's security. XChaCha20 uses the ChaCha20 permutation to map the
key and first 128 nonce bits to a 256-bit subkey. Then, it does the
ChaCha20 stream cipher with the subkey and remaining 64 bits of nonce.
We need XChaCha support in order to add support for the Adiantum
encryption mode. Note that to meet our performance requirements, we
actually plan to primarily use the variant XChaCha12. But we believe
it's wise to first add XChaCha20 as a baseline with a higher security
margin, in case there are any situations where it can be used.
Supporting both variants is straightforward.
Since XChaCha20's subkey differs for each request, XChaCha20 can't be a
template that wraps ChaCha20; that would require re-keying the
underlying ChaCha20 for every request, which wouldn't be thread-safe.
Instead, we make XChaCha20 its own top-level algorithm which calls the
ChaCha20 streaming implementation internally.
Similar to the existing ChaCha20 implementation, we define the IV to be
the nonce and stream position concatenated together. This allows users
to seek to any position in the stream.
I considered splitting the code into separate chacha20-common, chacha20,
and xchacha20 modules, so that chacha20 and xchacha20 could be
enabled/disabled independently. However, since nearly all the code is
shared anyway, I ultimately decided there would have been little benefit
to the added complexity of separate modules.
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Martin Willi <martin@strongswan.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2018-11-17 09:26:20 +08:00
|
|
|
/* Generate the stream and XOR it with the data */
|
2018-11-17 09:26:21 +08:00
|
|
|
return chacha_stream_xor(req, &subctx, real_iv);
|
2015-06-01 19:43:56 +08:00
|
|
|
}
|
crypto: chacha20-generic - add XChaCha20 support
Add support for the XChaCha20 stream cipher. XChaCha20 is the
application of the XSalsa20 construction
(https://cr.yp.to/snuffle/xsalsa-20081128.pdf) to ChaCha20 rather than
to Salsa20. XChaCha20 extends ChaCha20's nonce length from 64 bits (or
96 bits, depending on convention) to 192 bits, while provably retaining
ChaCha20's security. XChaCha20 uses the ChaCha20 permutation to map the
key and first 128 nonce bits to a 256-bit subkey. Then, it does the
ChaCha20 stream cipher with the subkey and remaining 64 bits of nonce.
We need XChaCha support in order to add support for the Adiantum
encryption mode. Note that to meet our performance requirements, we
actually plan to primarily use the variant XChaCha12. But we believe
it's wise to first add XChaCha20 as a baseline with a higher security
margin, in case there are any situations where it can be used.
Supporting both variants is straightforward.
Since XChaCha20's subkey differs for each request, XChaCha20 can't be a
template that wraps ChaCha20; that would require re-keying the
underlying ChaCha20 for every request, which wouldn't be thread-safe.
Instead, we make XChaCha20 its own top-level algorithm which calls the
ChaCha20 streaming implementation internally.
Similar to the existing ChaCha20 implementation, we define the IV to be
the nonce and stream position concatenated together. This allows users
to seek to any position in the stream.
I considered splitting the code into separate chacha20-common, chacha20,
and xchacha20 modules, so that chacha20 and xchacha20 could be
enabled/disabled independently. However, since nearly all the code is
shared anyway, I ultimately decided there would have been little benefit
to the added complexity of separate modules.
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Martin Willi <martin@strongswan.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2018-11-17 09:26:20 +08:00
|
|
|
|
|
|
|
|
static struct skcipher_alg algs[] = {
|
|
|
|
|
{
|
|
|
|
|
.base.cra_name = "chacha20",
|
|
|
|
|
.base.cra_driver_name = "chacha20-generic",
|
|
|
|
|
.base.cra_priority = 100,
|
|
|
|
|
.base.cra_blocksize = 1,
|
2018-11-17 09:26:21 +08:00
|
|
|
.base.cra_ctxsize = sizeof(struct chacha_ctx),
|
crypto: chacha20-generic - add XChaCha20 support
Add support for the XChaCha20 stream cipher. XChaCha20 is the
application of the XSalsa20 construction
(https://cr.yp.to/snuffle/xsalsa-20081128.pdf) to ChaCha20 rather than
to Salsa20. XChaCha20 extends ChaCha20's nonce length from 64 bits (or
96 bits, depending on convention) to 192 bits, while provably retaining
ChaCha20's security. XChaCha20 uses the ChaCha20 permutation to map the
key and first 128 nonce bits to a 256-bit subkey. Then, it does the
ChaCha20 stream cipher with the subkey and remaining 64 bits of nonce.
We need XChaCha support in order to add support for the Adiantum
encryption mode. Note that to meet our performance requirements, we
actually plan to primarily use the variant XChaCha12. But we believe
it's wise to first add XChaCha20 as a baseline with a higher security
margin, in case there are any situations where it can be used.
Supporting both variants is straightforward.
Since XChaCha20's subkey differs for each request, XChaCha20 can't be a
template that wraps ChaCha20; that would require re-keying the
underlying ChaCha20 for every request, which wouldn't be thread-safe.
Instead, we make XChaCha20 its own top-level algorithm which calls the
ChaCha20 streaming implementation internally.
Similar to the existing ChaCha20 implementation, we define the IV to be
the nonce and stream position concatenated together. This allows users
to seek to any position in the stream.
I considered splitting the code into separate chacha20-common, chacha20,
and xchacha20 modules, so that chacha20 and xchacha20 could be
enabled/disabled independently. However, since nearly all the code is
shared anyway, I ultimately decided there would have been little benefit
to the added complexity of separate modules.
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Martin Willi <martin@strongswan.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2018-11-17 09:26:20 +08:00
|
|
|
.base.cra_module = THIS_MODULE,
|
|
|
|
|
|
2018-11-17 09:26:21 +08:00
|
|
|
.min_keysize = CHACHA_KEY_SIZE,
|
|
|
|
|
.max_keysize = CHACHA_KEY_SIZE,
|
|
|
|
|
.ivsize = CHACHA_IV_SIZE,
|
|
|
|
|
.chunksize = CHACHA_BLOCK_SIZE,
|
2019-11-18 15:21:29 +08:00
|
|
|
.setkey = chacha20_setkey,
|
2018-11-17 09:26:21 +08:00
|
|
|
.encrypt = crypto_chacha_crypt,
|
|
|
|
|
.decrypt = crypto_chacha_crypt,
|
crypto: chacha20-generic - add XChaCha20 support
Add support for the XChaCha20 stream cipher. XChaCha20 is the
application of the XSalsa20 construction
(https://cr.yp.to/snuffle/xsalsa-20081128.pdf) to ChaCha20 rather than
to Salsa20. XChaCha20 extends ChaCha20's nonce length from 64 bits (or
96 bits, depending on convention) to 192 bits, while provably retaining
ChaCha20's security. XChaCha20 uses the ChaCha20 permutation to map the
key and first 128 nonce bits to a 256-bit subkey. Then, it does the
ChaCha20 stream cipher with the subkey and remaining 64 bits of nonce.
We need XChaCha support in order to add support for the Adiantum
encryption mode. Note that to meet our performance requirements, we
actually plan to primarily use the variant XChaCha12. But we believe
it's wise to first add XChaCha20 as a baseline with a higher security
margin, in case there are any situations where it can be used.
Supporting both variants is straightforward.
Since XChaCha20's subkey differs for each request, XChaCha20 can't be a
template that wraps ChaCha20; that would require re-keying the
underlying ChaCha20 for every request, which wouldn't be thread-safe.
Instead, we make XChaCha20 its own top-level algorithm which calls the
ChaCha20 streaming implementation internally.
Similar to the existing ChaCha20 implementation, we define the IV to be
the nonce and stream position concatenated together. This allows users
to seek to any position in the stream.
I considered splitting the code into separate chacha20-common, chacha20,
and xchacha20 modules, so that chacha20 and xchacha20 could be
enabled/disabled independently. However, since nearly all the code is
shared anyway, I ultimately decided there would have been little benefit
to the added complexity of separate modules.
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Martin Willi <martin@strongswan.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2018-11-17 09:26:20 +08:00
|
|
|
}, {
|
|
|
|
|
.base.cra_name = "xchacha20",
|
|
|
|
|
.base.cra_driver_name = "xchacha20-generic",
|
|
|
|
|
.base.cra_priority = 100,
|
|
|
|
|
.base.cra_blocksize = 1,
|
2018-11-17 09:26:21 +08:00
|
|
|
.base.cra_ctxsize = sizeof(struct chacha_ctx),
|
crypto: chacha20-generic - add XChaCha20 support
Add support for the XChaCha20 stream cipher. XChaCha20 is the
application of the XSalsa20 construction
(https://cr.yp.to/snuffle/xsalsa-20081128.pdf) to ChaCha20 rather than
to Salsa20. XChaCha20 extends ChaCha20's nonce length from 64 bits (or
96 bits, depending on convention) to 192 bits, while provably retaining
ChaCha20's security. XChaCha20 uses the ChaCha20 permutation to map the
key and first 128 nonce bits to a 256-bit subkey. Then, it does the
ChaCha20 stream cipher with the subkey and remaining 64 bits of nonce.
We need XChaCha support in order to add support for the Adiantum
encryption mode. Note that to meet our performance requirements, we
actually plan to primarily use the variant XChaCha12. But we believe
it's wise to first add XChaCha20 as a baseline with a higher security
margin, in case there are any situations where it can be used.
Supporting both variants is straightforward.
Since XChaCha20's subkey differs for each request, XChaCha20 can't be a
template that wraps ChaCha20; that would require re-keying the
underlying ChaCha20 for every request, which wouldn't be thread-safe.
Instead, we make XChaCha20 its own top-level algorithm which calls the
ChaCha20 streaming implementation internally.
Similar to the existing ChaCha20 implementation, we define the IV to be
the nonce and stream position concatenated together. This allows users
to seek to any position in the stream.
I considered splitting the code into separate chacha20-common, chacha20,
and xchacha20 modules, so that chacha20 and xchacha20 could be
enabled/disabled independently. However, since nearly all the code is
shared anyway, I ultimately decided there would have been little benefit
to the added complexity of separate modules.
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Martin Willi <martin@strongswan.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2018-11-17 09:26:20 +08:00
|
|
|
.base.cra_module = THIS_MODULE,
|
|
|
|
|
|
2018-11-17 09:26:21 +08:00
|
|
|
.min_keysize = CHACHA_KEY_SIZE,
|
|
|
|
|
.max_keysize = CHACHA_KEY_SIZE,
|
|
|
|
|
.ivsize = XCHACHA_IV_SIZE,
|
|
|
|
|
.chunksize = CHACHA_BLOCK_SIZE,
|
2019-11-18 15:21:29 +08:00
|
|
|
.setkey = chacha20_setkey,
|
2018-11-17 09:26:21 +08:00
|
|
|
.encrypt = crypto_xchacha_crypt,
|
|
|
|
|
.decrypt = crypto_xchacha_crypt,
|
crypto: chacha - add XChaCha12 support
Now that the generic implementation of ChaCha20 has been refactored to
allow varying the number of rounds, add support for XChaCha12, which is
the XSalsa construction applied to ChaCha12. ChaCha12 is one of the
three ciphers specified by the original ChaCha paper
(https://cr.yp.to/chacha/chacha-20080128.pdf: "ChaCha, a variant of
Salsa20"), alongside ChaCha8 and ChaCha20. ChaCha12 is faster than
ChaCha20 but has a lower, but still large, security margin.
We need XChaCha12 support so that it can be used in the Adiantum
encryption mode, which enables disk/file encryption on low-end mobile
devices where AES-XTS is too slow as the CPUs lack AES instructions.
We'd prefer XChaCha20 (the more popular variant), but it's too slow on
some of our target devices, so at least in some cases we do need the
XChaCha12-based version. In more detail, the problem is that Adiantum
is still much slower than we're happy with, and encryption still has a
quite noticeable effect on the feel of low-end devices. Users and
vendors push back hard against encryption that degrades the user
experience, which always risks encryption being disabled entirely. So
we need to choose the fastest option that gives us a solid margin of
security, and here that's XChaCha12. The best known attack on ChaCha
breaks only 7 rounds and has 2^235 time complexity, so ChaCha12's
security margin is still better than AES-256's. Much has been learned
about cryptanalysis of ARX ciphers since Salsa20 was originally designed
in 2005, and it now seems we can be comfortable with a smaller number of
rounds. The eSTREAM project also suggests the 12-round version of
Salsa20 as providing the best balance among the different variants:
combining very good performance with a "comfortable margin of security".
Note that it would be trivial to add vanilla ChaCha12 in addition to
XChaCha12. However, it's unneeded for now and therefore is omitted.
As discussed in the patch that introduced XChaCha20 support, I
considered splitting the code into separate chacha-common, chacha20,
xchacha20, and xchacha12 modules, so that these algorithms could be
enabled/disabled independently. However, since nearly all the code is
shared anyway, I ultimately decided there would have been little benefit
to the added complexity.
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Martin Willi <martin@strongswan.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2018-11-17 09:26:22 +08:00
|
|
|
}, {
|
|
|
|
|
.base.cra_name = "xchacha12",
|
|
|
|
|
.base.cra_driver_name = "xchacha12-generic",
|
|
|
|
|
.base.cra_priority = 100,
|
|
|
|
|
.base.cra_blocksize = 1,
|
|
|
|
|
.base.cra_ctxsize = sizeof(struct chacha_ctx),
|
|
|
|
|
.base.cra_module = THIS_MODULE,
|
|
|
|
|
|
|
|
|
|
.min_keysize = CHACHA_KEY_SIZE,
|
|
|
|
|
.max_keysize = CHACHA_KEY_SIZE,
|
|
|
|
|
.ivsize = XCHACHA_IV_SIZE,
|
|
|
|
|
.chunksize = CHACHA_BLOCK_SIZE,
|
2019-11-18 15:21:29 +08:00
|
|
|
.setkey = chacha12_setkey,
|
crypto: chacha - add XChaCha12 support
Now that the generic implementation of ChaCha20 has been refactored to
allow varying the number of rounds, add support for XChaCha12, which is
the XSalsa construction applied to ChaCha12. ChaCha12 is one of the
three ciphers specified by the original ChaCha paper
(https://cr.yp.to/chacha/chacha-20080128.pdf: "ChaCha, a variant of
Salsa20"), alongside ChaCha8 and ChaCha20. ChaCha12 is faster than
ChaCha20 but has a lower, but still large, security margin.
We need XChaCha12 support so that it can be used in the Adiantum
encryption mode, which enables disk/file encryption on low-end mobile
devices where AES-XTS is too slow as the CPUs lack AES instructions.
We'd prefer XChaCha20 (the more popular variant), but it's too slow on
some of our target devices, so at least in some cases we do need the
XChaCha12-based version. In more detail, the problem is that Adiantum
is still much slower than we're happy with, and encryption still has a
quite noticeable effect on the feel of low-end devices. Users and
vendors push back hard against encryption that degrades the user
experience, which always risks encryption being disabled entirely. So
we need to choose the fastest option that gives us a solid margin of
security, and here that's XChaCha12. The best known attack on ChaCha
breaks only 7 rounds and has 2^235 time complexity, so ChaCha12's
security margin is still better than AES-256's. Much has been learned
about cryptanalysis of ARX ciphers since Salsa20 was originally designed
in 2005, and it now seems we can be comfortable with a smaller number of
rounds. The eSTREAM project also suggests the 12-round version of
Salsa20 as providing the best balance among the different variants:
combining very good performance with a "comfortable margin of security".
Note that it would be trivial to add vanilla ChaCha12 in addition to
XChaCha12. However, it's unneeded for now and therefore is omitted.
As discussed in the patch that introduced XChaCha20 support, I
considered splitting the code into separate chacha-common, chacha20,
xchacha20, and xchacha12 modules, so that these algorithms could be
enabled/disabled independently. However, since nearly all the code is
shared anyway, I ultimately decided there would have been little benefit
to the added complexity.
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Martin Willi <martin@strongswan.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2018-11-17 09:26:22 +08:00
|
|
|
.encrypt = crypto_xchacha_crypt,
|
|
|
|
|
.decrypt = crypto_xchacha_crypt,
|
crypto: chacha20-generic - add XChaCha20 support
Add support for the XChaCha20 stream cipher. XChaCha20 is the
application of the XSalsa20 construction
(https://cr.yp.to/snuffle/xsalsa-20081128.pdf) to ChaCha20 rather than
to Salsa20. XChaCha20 extends ChaCha20's nonce length from 64 bits (or
96 bits, depending on convention) to 192 bits, while provably retaining
ChaCha20's security. XChaCha20 uses the ChaCha20 permutation to map the
key and first 128 nonce bits to a 256-bit subkey. Then, it does the
ChaCha20 stream cipher with the subkey and remaining 64 bits of nonce.
We need XChaCha support in order to add support for the Adiantum
encryption mode. Note that to meet our performance requirements, we
actually plan to primarily use the variant XChaCha12. But we believe
it's wise to first add XChaCha20 as a baseline with a higher security
margin, in case there are any situations where it can be used.
Supporting both variants is straightforward.
Since XChaCha20's subkey differs for each request, XChaCha20 can't be a
template that wraps ChaCha20; that would require re-keying the
underlying ChaCha20 for every request, which wouldn't be thread-safe.
Instead, we make XChaCha20 its own top-level algorithm which calls the
ChaCha20 streaming implementation internally.
Similar to the existing ChaCha20 implementation, we define the IV to be
the nonce and stream position concatenated together. This allows users
to seek to any position in the stream.
I considered splitting the code into separate chacha20-common, chacha20,
and xchacha20 modules, so that chacha20 and xchacha20 could be
enabled/disabled independently. However, since nearly all the code is
shared anyway, I ultimately decided there would have been little benefit
to the added complexity of separate modules.
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Martin Willi <martin@strongswan.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2018-11-17 09:26:20 +08:00
|
|
|
}
|
2015-06-01 19:43:56 +08:00
|
|
|
};
|
|
|
|
|
|
2018-11-17 09:26:21 +08:00
|
|
|
static int __init chacha_generic_mod_init(void)
|
2015-06-01 19:43:56 +08:00
|
|
|
{
|
crypto: chacha20-generic - add XChaCha20 support
Add support for the XChaCha20 stream cipher. XChaCha20 is the
application of the XSalsa20 construction
(https://cr.yp.to/snuffle/xsalsa-20081128.pdf) to ChaCha20 rather than
to Salsa20. XChaCha20 extends ChaCha20's nonce length from 64 bits (or
96 bits, depending on convention) to 192 bits, while provably retaining
ChaCha20's security. XChaCha20 uses the ChaCha20 permutation to map the
key and first 128 nonce bits to a 256-bit subkey. Then, it does the
ChaCha20 stream cipher with the subkey and remaining 64 bits of nonce.
We need XChaCha support in order to add support for the Adiantum
encryption mode. Note that to meet our performance requirements, we
actually plan to primarily use the variant XChaCha12. But we believe
it's wise to first add XChaCha20 as a baseline with a higher security
margin, in case there are any situations where it can be used.
Supporting both variants is straightforward.
Since XChaCha20's subkey differs for each request, XChaCha20 can't be a
template that wraps ChaCha20; that would require re-keying the
underlying ChaCha20 for every request, which wouldn't be thread-safe.
Instead, we make XChaCha20 its own top-level algorithm which calls the
ChaCha20 streaming implementation internally.
Similar to the existing ChaCha20 implementation, we define the IV to be
the nonce and stream position concatenated together. This allows users
to seek to any position in the stream.
I considered splitting the code into separate chacha20-common, chacha20,
and xchacha20 modules, so that chacha20 and xchacha20 could be
enabled/disabled independently. However, since nearly all the code is
shared anyway, I ultimately decided there would have been little benefit
to the added complexity of separate modules.
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Martin Willi <martin@strongswan.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2018-11-17 09:26:20 +08:00
|
|
|
return crypto_register_skciphers(algs, ARRAY_SIZE(algs));
|
2015-06-01 19:43:56 +08:00
|
|
|
}
|
|
|
|
|
|
2018-11-17 09:26:21 +08:00
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static void __exit chacha_generic_mod_fini(void)
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2015-06-01 19:43:56 +08:00
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{
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crypto: chacha20-generic - add XChaCha20 support
Add support for the XChaCha20 stream cipher. XChaCha20 is the
application of the XSalsa20 construction
(https://cr.yp.to/snuffle/xsalsa-20081128.pdf) to ChaCha20 rather than
to Salsa20. XChaCha20 extends ChaCha20's nonce length from 64 bits (or
96 bits, depending on convention) to 192 bits, while provably retaining
ChaCha20's security. XChaCha20 uses the ChaCha20 permutation to map the
key and first 128 nonce bits to a 256-bit subkey. Then, it does the
ChaCha20 stream cipher with the subkey and remaining 64 bits of nonce.
We need XChaCha support in order to add support for the Adiantum
encryption mode. Note that to meet our performance requirements, we
actually plan to primarily use the variant XChaCha12. But we believe
it's wise to first add XChaCha20 as a baseline with a higher security
margin, in case there are any situations where it can be used.
Supporting both variants is straightforward.
Since XChaCha20's subkey differs for each request, XChaCha20 can't be a
template that wraps ChaCha20; that would require re-keying the
underlying ChaCha20 for every request, which wouldn't be thread-safe.
Instead, we make XChaCha20 its own top-level algorithm which calls the
ChaCha20 streaming implementation internally.
Similar to the existing ChaCha20 implementation, we define the IV to be
the nonce and stream position concatenated together. This allows users
to seek to any position in the stream.
I considered splitting the code into separate chacha20-common, chacha20,
and xchacha20 modules, so that chacha20 and xchacha20 could be
enabled/disabled independently. However, since nearly all the code is
shared anyway, I ultimately decided there would have been little benefit
to the added complexity of separate modules.
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Martin Willi <martin@strongswan.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2018-11-17 09:26:20 +08:00
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crypto_unregister_skciphers(algs, ARRAY_SIZE(algs));
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2015-06-01 19:43:56 +08:00
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}
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2019-04-12 12:57:42 +08:00
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subsys_initcall(chacha_generic_mod_init);
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2018-11-17 09:26:21 +08:00
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module_exit(chacha_generic_mod_fini);
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2015-06-01 19:43:56 +08:00
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MODULE_LICENSE("GPL");
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MODULE_AUTHOR("Martin Willi <martin@strongswan.org>");
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2018-11-17 09:26:21 +08:00
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MODULE_DESCRIPTION("ChaCha and XChaCha stream ciphers (generic)");
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2015-06-01 19:43:56 +08:00
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MODULE_ALIAS_CRYPTO("chacha20");
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MODULE_ALIAS_CRYPTO("chacha20-generic");
|
crypto: chacha20-generic - add XChaCha20 support
Add support for the XChaCha20 stream cipher. XChaCha20 is the
application of the XSalsa20 construction
(https://cr.yp.to/snuffle/xsalsa-20081128.pdf) to ChaCha20 rather than
to Salsa20. XChaCha20 extends ChaCha20's nonce length from 64 bits (or
96 bits, depending on convention) to 192 bits, while provably retaining
ChaCha20's security. XChaCha20 uses the ChaCha20 permutation to map the
key and first 128 nonce bits to a 256-bit subkey. Then, it does the
ChaCha20 stream cipher with the subkey and remaining 64 bits of nonce.
We need XChaCha support in order to add support for the Adiantum
encryption mode. Note that to meet our performance requirements, we
actually plan to primarily use the variant XChaCha12. But we believe
it's wise to first add XChaCha20 as a baseline with a higher security
margin, in case there are any situations where it can be used.
Supporting both variants is straightforward.
Since XChaCha20's subkey differs for each request, XChaCha20 can't be a
template that wraps ChaCha20; that would require re-keying the
underlying ChaCha20 for every request, which wouldn't be thread-safe.
Instead, we make XChaCha20 its own top-level algorithm which calls the
ChaCha20 streaming implementation internally.
Similar to the existing ChaCha20 implementation, we define the IV to be
the nonce and stream position concatenated together. This allows users
to seek to any position in the stream.
I considered splitting the code into separate chacha20-common, chacha20,
and xchacha20 modules, so that chacha20 and xchacha20 could be
enabled/disabled independently. However, since nearly all the code is
shared anyway, I ultimately decided there would have been little benefit
to the added complexity of separate modules.
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Martin Willi <martin@strongswan.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2018-11-17 09:26:20 +08:00
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MODULE_ALIAS_CRYPTO("xchacha20");
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MODULE_ALIAS_CRYPTO("xchacha20-generic");
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crypto: chacha - add XChaCha12 support
Now that the generic implementation of ChaCha20 has been refactored to
allow varying the number of rounds, add support for XChaCha12, which is
the XSalsa construction applied to ChaCha12. ChaCha12 is one of the
three ciphers specified by the original ChaCha paper
(https://cr.yp.to/chacha/chacha-20080128.pdf: "ChaCha, a variant of
Salsa20"), alongside ChaCha8 and ChaCha20. ChaCha12 is faster than
ChaCha20 but has a lower, but still large, security margin.
We need XChaCha12 support so that it can be used in the Adiantum
encryption mode, which enables disk/file encryption on low-end mobile
devices where AES-XTS is too slow as the CPUs lack AES instructions.
We'd prefer XChaCha20 (the more popular variant), but it's too slow on
some of our target devices, so at least in some cases we do need the
XChaCha12-based version. In more detail, the problem is that Adiantum
is still much slower than we're happy with, and encryption still has a
quite noticeable effect on the feel of low-end devices. Users and
vendors push back hard against encryption that degrades the user
experience, which always risks encryption being disabled entirely. So
we need to choose the fastest option that gives us a solid margin of
security, and here that's XChaCha12. The best known attack on ChaCha
breaks only 7 rounds and has 2^235 time complexity, so ChaCha12's
security margin is still better than AES-256's. Much has been learned
about cryptanalysis of ARX ciphers since Salsa20 was originally designed
in 2005, and it now seems we can be comfortable with a smaller number of
rounds. The eSTREAM project also suggests the 12-round version of
Salsa20 as providing the best balance among the different variants:
combining very good performance with a "comfortable margin of security".
Note that it would be trivial to add vanilla ChaCha12 in addition to
XChaCha12. However, it's unneeded for now and therefore is omitted.
As discussed in the patch that introduced XChaCha20 support, I
considered splitting the code into separate chacha-common, chacha20,
xchacha20, and xchacha12 modules, so that these algorithms could be
enabled/disabled independently. However, since nearly all the code is
shared anyway, I ultimately decided there would have been little benefit
to the added complexity.
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Martin Willi <martin@strongswan.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2018-11-17 09:26:22 +08:00
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MODULE_ALIAS_CRYPTO("xchacha12");
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MODULE_ALIAS_CRYPTO("xchacha12-generic");
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