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ChaCha20: move working state from ctx to stack

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No need to keep it around.
This commit is contained in:
Manuel Pégourié-Gonnard 2018-05-24 17:23:41 +02:00
parent 9620f9b99e
commit 98fae6d800
2 changed files with 26 additions and 29 deletions
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3
include/mbedtls/chacha20.h
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@ -54,8 +54,7 @@ extern "C" {
typedef struct typedef struct
{ {
uint32_t initial_state[16]; /*! The initial state (before round operations). */ uint32_t state[16]; /*! The state (before round operations). */
uint32_t working_state[16]; /*! The working state (after round operations). */
uint8_t keystream8[64]; /*! Leftover keystream bytes. */ uint8_t keystream8[64]; /*! Leftover keystream bytes. */
size_t keystream_bytes_used; /*! Number of keystream bytes already used. */ size_t keystream_bytes_used; /*! Number of keystream bytes already used. */
} }

52
library/chacha20.c
View File

@ -128,15 +128,13 @@ static void chacha20_inner_block( uint32_t state[16] )
* \brief Generates a keystream block. * \brief Generates a keystream block.
* *
* \param initial_state The initial ChaCha20 state (containing the key, nonce, counter). * \param initial_state The initial ChaCha20 state (containing the key, nonce, counter).
* \param working_state This state is used as a temporary working area.
* \param keystream Generated keystream bytes are written to this buffer. * \param keystream Generated keystream bytes are written to this buffer.
*/ */
static void chacha20_block( const uint32_t initial_state[16], static void chacha20_block( const uint32_t initial_state[16],
uint32_t working_state[16],
unsigned char keystream[64] ) unsigned char keystream[64] )
{ {
uint32_t working_state[16];
size_t i; size_t i;
size_t offset;
memcpy( working_state, memcpy( working_state,
initial_state, initial_state,
@ -164,21 +162,22 @@ static void chacha20_block( const uint32_t initial_state[16],
for ( i = 0U; i < 16; i++ ) for ( i = 0U; i < 16; i++ )
{ {
offset = i * 4U; size_t offset = i * 4U;
keystream[offset ] = (unsigned char) working_state[i]; keystream[offset ] = (unsigned char) working_state[i];
keystream[offset + 1U] = (unsigned char) ( working_state[i] >> 8 ); keystream[offset + 1U] = (unsigned char) ( working_state[i] >> 8 );
keystream[offset + 2U] = (unsigned char) ( working_state[i] >> 16 ); keystream[offset + 2U] = (unsigned char) ( working_state[i] >> 16 );
keystream[offset + 3U] = (unsigned char) ( working_state[i] >> 24 ); keystream[offset + 3U] = (unsigned char) ( working_state[i] >> 24 );
} }
mbedtls_platform_zeroize( working_state, sizeof( working_state ) );
} }
void mbedtls_chacha20_init( mbedtls_chacha20_context *ctx ) void mbedtls_chacha20_init( mbedtls_chacha20_context *ctx )
{ {
if ( ctx != NULL ) if ( ctx != NULL )
{ {
mbedtls_platform_zeroize( ctx->initial_state, sizeof( ctx->initial_state ) ); mbedtls_platform_zeroize( ctx->state, sizeof( ctx->state ) );
mbedtls_platform_zeroize( ctx->working_state, sizeof( ctx->working_state ) );
mbedtls_platform_zeroize( ctx->keystream8, sizeof( ctx->keystream8 ) ); mbedtls_platform_zeroize( ctx->keystream8, sizeof( ctx->keystream8 ) );
/* Initially, there's no keystream bytes available */ /* Initially, there's no keystream bytes available */
@ -203,20 +202,20 @@ int mbedtls_chacha20_setkey( mbedtls_chacha20_context *ctx,
} }
/* ChaCha20 constants - the string "expand 32-byte k" */ /* ChaCha20 constants - the string "expand 32-byte k" */
ctx->initial_state[0] = 0x61707865; ctx->state[0] = 0x61707865;
ctx->initial_state[1] = 0x3320646e; ctx->state[1] = 0x3320646e;
ctx->initial_state[2] = 0x79622d32; ctx->state[2] = 0x79622d32;
ctx->initial_state[3] = 0x6b206574; ctx->state[3] = 0x6b206574;
/* Set key */ /* Set key */
ctx->initial_state[4] = BYTES_TO_U32_LE( key, 0 ); ctx->state[4] = BYTES_TO_U32_LE( key, 0 );
ctx->initial_state[5] = BYTES_TO_U32_LE( key, 4 ); ctx->state[5] = BYTES_TO_U32_LE( key, 4 );
ctx->initial_state[6] = BYTES_TO_U32_LE( key, 8 ); ctx->state[6] = BYTES_TO_U32_LE( key, 8 );
ctx->initial_state[7] = BYTES_TO_U32_LE( key, 12 ); ctx->state[7] = BYTES_TO_U32_LE( key, 12 );
ctx->initial_state[8] = BYTES_TO_U32_LE( key, 16 ); ctx->state[8] = BYTES_TO_U32_LE( key, 16 );
ctx->initial_state[9] = BYTES_TO_U32_LE( key, 20 ); ctx->state[9] = BYTES_TO_U32_LE( key, 20 );
ctx->initial_state[10] = BYTES_TO_U32_LE( key, 24 ); ctx->state[10] = BYTES_TO_U32_LE( key, 24 );
ctx->initial_state[11] = BYTES_TO_U32_LE( key, 28 ); ctx->state[11] = BYTES_TO_U32_LE( key, 28 );
return( 0 ); return( 0 );
} }
@ -231,14 +230,13 @@ int mbedtls_chacha20_starts( mbedtls_chacha20_context* ctx,
} }
/* Counter */ /* Counter */
ctx->initial_state[12] = counter; ctx->state[12] = counter;
/* Nonce */ /* Nonce */
ctx->initial_state[13] = BYTES_TO_U32_LE( nonce, 0 ); ctx->state[13] = BYTES_TO_U32_LE( nonce, 0 );
ctx->initial_state[14] = BYTES_TO_U32_LE( nonce, 4 ); ctx->state[14] = BYTES_TO_U32_LE( nonce, 4 );
ctx->initial_state[15] = BYTES_TO_U32_LE( nonce, 8 ); ctx->state[15] = BYTES_TO_U32_LE( nonce, 8 );
mbedtls_platform_zeroize( ctx->working_state, sizeof( ctx->working_state ) );
mbedtls_platform_zeroize( ctx->keystream8, sizeof( ctx->keystream8 ) ); mbedtls_platform_zeroize( ctx->keystream8, sizeof( ctx->keystream8 ) );
/* Initially, there's no keystream bytes available */ /* Initially, there's no keystream bytes available */
@ -279,8 +277,8 @@ int mbedtls_chacha20_update( mbedtls_chacha20_context *ctx,
while ( size >= CHACHA20_BLOCK_SIZE_BYTES ) while ( size >= CHACHA20_BLOCK_SIZE_BYTES )
{ {
/* Generate new keystream block and increment counter */ /* Generate new keystream block and increment counter */
chacha20_block( ctx->initial_state, ctx->working_state, ctx->keystream8 ); chacha20_block( ctx->state, ctx->keystream8 );
ctx->initial_state[CHACHA20_CTR_INDEX]++; ctx->state[CHACHA20_CTR_INDEX]++;
for ( i = 0U; i < 64U; i += 8U ) for ( i = 0U; i < 64U; i += 8U )
{ {
@ -302,8 +300,8 @@ int mbedtls_chacha20_update( mbedtls_chacha20_context *ctx,
if ( size > 0U ) if ( size > 0U )
{ {
/* Generate new keystream block and increment counter */ /* Generate new keystream block and increment counter */
chacha20_block( ctx->initial_state, ctx->working_state, ctx->keystream8 ); chacha20_block( ctx->state, ctx->keystream8 );
ctx->initial_state[CHACHA20_CTR_INDEX]++; ctx->state[CHACHA20_CTR_INDEX]++;
for ( i = 0U; i < size; i++) for ( i = 0U; i < size; i++)
{ {