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ChaCha20: allow in-place en/decryption

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All other ciphers so far allow this. In particular, the TLS layer depends on
this, despite what's documented in the Cipher layer, see
https://github.com/ARMmbed/mbedtls/issues/1085
https://github.com/ARMmbed/mbedtls/issues/1087

Also, this can be useful for implementing chachapoly without depending on the
semi-internal function keystream_block(), see next commit.
This commit is contained in:
Manuel Pégourié-Gonnard 2018-05-07 11:57:05 +02:00
parent dca3a5d884
commit 502f189253
2 changed files with 15 additions and 17 deletions
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5
include/mbedtls/chacha20.h
View file

@ -133,9 +133,8 @@ int mbedtls_chacha20_keystream_block( const mbedtls_chacha20_context *ctx,
* *
* This function is used to both encrypt and decrypt data. * This function is used to both encrypt and decrypt data.
* *
* \note The \p input and \p output buffers may overlap, but only * \note The \p input and \p output pointers must either be equal or
* if input >= output (i.e. only if input points ahead of * point to non-overlapping buffers.
* the output pointer).
* *
* \note mbedtls_chacha20_setkey and mbedtls_chacha20_starts must be * \note mbedtls_chacha20_setkey and mbedtls_chacha20_starts must be
* called at least once to setup the context before this function * called at least once to setup the context before this function

27
library/chacha20.c
View file

@ -314,23 +314,22 @@ int mbedtls_chacha20_update( mbedtls_chacha20_context *ctx,
/* Process full blocks */ /* Process full blocks */
while ( size >= CHACHA20_BLOCK_SIZE_BYTES ) while ( size >= CHACHA20_BLOCK_SIZE_BYTES )
{ {
mbedtls_chacha20_block( ctx->initial_state, ctx->working_state, &output[offset] ); /* Generate new keystream block and increment counter */
mbedtls_chacha20_block( ctx->initial_state, ctx->working_state, ctx->keystream8 );
ctx->initial_state[CHACHA20_CTR_INDEX]++;
for ( i = 0U; i < 64U; i += 8U ) for ( i = 0U; i < 64U; i += 8U )
{ {
output[offset + i ] ^= input[offset + i ]; output[offset + i ] = input[offset + i ] ^ ctx->keystream8[i ];
output[offset + i + 1U] ^= input[offset + i + 1U]; output[offset + i + 1U ] = input[offset + i + 1U ] ^ ctx->keystream8[i + 1U ];
output[offset + i + 2U] ^= input[offset + i + 2U]; output[offset + i + 2U ] = input[offset + i + 2U ] ^ ctx->keystream8[i + 2U ];
output[offset + i + 3U] ^= input[offset + i + 3U]; output[offset + i + 3U ] = input[offset + i + 3U ] ^ ctx->keystream8[i + 3U ];
output[offset + i + 4U] ^= input[offset + i + 4U]; output[offset + i + 4U ] = input[offset + i + 4U ] ^ ctx->keystream8[i + 4U ];
output[offset + i + 5U] ^= input[offset + i + 5U]; output[offset + i + 5U ] = input[offset + i + 5U ] ^ ctx->keystream8[i + 5U ];
output[offset + i + 6U] ^= input[offset + i + 6U]; output[offset + i + 6U ] = input[offset + i + 6U ] ^ ctx->keystream8[i + 6U ];
output[offset + i + 7U] ^= input[offset + i + 7U]; output[offset + i + 7U ] = input[offset + i + 7U ] ^ ctx->keystream8[i + 7U ];
} }
/* Increment counter */
ctx->initial_state[CHACHA20_CTR_INDEX]++;
offset += CHACHA20_BLOCK_SIZE_BYTES; offset += CHACHA20_BLOCK_SIZE_BYTES;
size -= CHACHA20_BLOCK_SIZE_BYTES; size -= CHACHA20_BLOCK_SIZE_BYTES;
} }
@ -338,7 +337,9 @@ int mbedtls_chacha20_update( mbedtls_chacha20_context *ctx,
/* Last (partial) block */ /* Last (partial) block */
if ( size > 0U ) if ( size > 0U )
{ {
/* Generate new keystream block and increment counter */
mbedtls_chacha20_block( ctx->initial_state, ctx->working_state, ctx->keystream8 ); mbedtls_chacha20_block( ctx->initial_state, ctx->working_state, ctx->keystream8 );
ctx->initial_state[CHACHA20_CTR_INDEX]++;
for ( i = 0U; i < size; i++) for ( i = 0U; i < size; i++)
{ {
@ -347,8 +348,6 @@ int mbedtls_chacha20_update( mbedtls_chacha20_context *ctx,
ctx->keystream_bytes_used = size; ctx->keystream_bytes_used = size;
/* Increment counter */
ctx->initial_state[CHACHA20_CTR_INDEX]++;
} }
return( 0 ); return( 0 );