On 16 October 2018 at 01:54, Eric Biggers <ebiggers@xxxxxxxxxx> wrote: > From: Eric Biggers <ebiggers@xxxxxxxxxx> > > Refactor the unkeyed permutation part of chacha20_block() into its own > function, then add hchacha20_block() which is the ChaCha equivalent of > HSalsa20 and is an intermediate step towards XChaCha20 (see > https://cr.yp.to/snuffle/xsalsa-20081128.pdf). HChaCha20 skips the > final addition of the initial state, and outputs only certain words of > the state. It should not be used for streaming directly. > > Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx> Reviewed-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> > --- > include/crypto/chacha20.h | 2 ++ > lib/chacha20.c | 50 ++++++++++++++++++++++++++++++++++----- > 2 files changed, 46 insertions(+), 6 deletions(-) > > diff --git a/include/crypto/chacha20.h b/include/crypto/chacha20.h > index f76302d99e2be..fbec4e6a87890 100644 > --- a/include/crypto/chacha20.h > +++ b/include/crypto/chacha20.h > @@ -19,6 +19,8 @@ struct chacha20_ctx { > }; > > void chacha20_block(u32 *state, u8 *stream); > +void hchacha20_block(const u32 *in, u32 *out); > + > void crypto_chacha20_init(u32 *state, struct chacha20_ctx *ctx, u8 *iv); > int crypto_chacha20_setkey(struct crypto_skcipher *tfm, const u8 *key, > unsigned int keysize); > diff --git a/lib/chacha20.c b/lib/chacha20.c > index d907fec6a9ed1..6a484e16171d1 100644 > --- a/lib/chacha20.c > +++ b/lib/chacha20.c > @@ -1,5 +1,5 @@ > /* > - * ChaCha20 256-bit cipher algorithm, RFC7539 > + * The "hash function" used as the core of the ChaCha20 stream cipher (RFC7539) > * > * Copyright (C) 2015 Martin Willi > * > @@ -16,14 +16,10 @@ > #include <asm/unaligned.h> > #include <crypto/chacha20.h> > > -void chacha20_block(u32 *state, u8 *stream) > +static void chacha20_permute(u32 *x) > { > - u32 x[16]; > int i; > > - for (i = 0; i < ARRAY_SIZE(x); i++) > - x[i] = state[i]; > - > for (i = 0; i < 20; i += 2) { > x[0] += x[4]; x[12] = rol32(x[12] ^ x[0], 16); > x[1] += x[5]; x[13] = rol32(x[13] ^ x[1], 16); > @@ -65,6 +61,25 @@ void chacha20_block(u32 *state, u8 *stream) > x[8] += x[13]; x[7] = rol32(x[7] ^ x[8], 7); > x[9] += x[14]; x[4] = rol32(x[4] ^ x[9], 7); > } > +} > + > +/** > + * chacha20_block - generate one keystream block and increment block counter > + * @state: input state matrix (16 32-bit words) > + * @stream: output keystream block (64 bytes) > + * > + * This is the ChaCha20 core, a function from 64-byte strings to 64-byte > + * strings. The caller has already converted the endianness of the input. This > + * function also handles incrementing the block counter in the input matrix. > + */ > +void chacha20_block(u32 *state, u8 *stream) > +{ > + u32 x[16]; > + int i; > + > + memcpy(x, state, 64); > + > + chacha20_permute(x); > > for (i = 0; i < ARRAY_SIZE(x); i++) > put_unaligned_le32(x[i] + state[i], &stream[i * sizeof(u32)]); > @@ -72,3 +87,26 @@ void chacha20_block(u32 *state, u8 *stream) > state[12]++; > } > EXPORT_SYMBOL(chacha20_block); > + > +/** > + * hchacha20_block - abbreviated ChaCha20 core, for XChaCha20 > + * @in: input state matrix (16 32-bit words) > + * @out: output (8 32-bit words) > + * > + * HChaCha20 is the ChaCha equivalent of HSalsa20 and is an intermediate step > + * towards XChaCha20 (see https://cr.yp.to/snuffle/xsalsa-20081128.pdf). > + * HChaCha20 skips the final addition of the initial state, and outputs only > + * certain words of the state. It should not be used for streaming directly. > + */ > +void hchacha20_block(const u32 *in, u32 *out) > +{ > + u32 x[16]; > + > + memcpy(x, in, 64); > + > + chacha20_permute(x); > + > + memcpy(&out[0], &x[0], 16); > + memcpy(&out[4], &x[12], 16); > +} > +EXPORT_SYMBOL(hchacha20_block); > -- > 2.19.1.331.ge82ca0e54c-goog > > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@xxxxxxxxxxxxxxxxxxx > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
