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[crypto] Simplify internal HMAC API

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Simplify the internal HMAC API so that the key is provided only at the
point of calling hmac_init(), and the (potentially reduced) key is
stored as part of the context for later use by hmac_final().

This simplifies the calling code, and avoids the need for callers such
as TLS to allocate a potentially variable length block in order to
retain a copy of the unmodified key.

Signed-off-by: Michael Brown <mcb30@ipxe.org>
This commit is contained in:
Michael Brown
2022-10-09 15:14:41 +01:00
parent 88419b608d
commit 007d3cb800
16 changed files with 142 additions and 163 deletions
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96
src/crypto/hmac.c
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@@ -46,94 +46,62 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
#include <ipxe/crypto.h>
#include <ipxe/hmac.h>
/**
* Reduce HMAC key length
*
* @v digest Digest algorithm to use
* @v digest_ctx Digest context
* @v key Key
* @v key_len Length of key
*/
static void hmac_reduce_key ( struct digest_algorithm *digest,
void *key, size_t *key_len ) {
uint8_t digest_ctx[digest->ctxsize];
digest_init ( digest, digest_ctx );
digest_update ( digest, digest_ctx, key, *key_len );
digest_final ( digest, digest_ctx, key );
*key_len = digest->digestsize;
}
/**
* Initialise HMAC
*
* @v digest Digest algorithm to use
* @v digest_ctx Digest context
* @v ctx HMAC context
* @v key Key
* @v key_len Length of key
*
* The length of the key should be less than the block size of the
* digest algorithm being used. (If the key length is greater, it
* will be replaced with its own digest, and key_len will be updated
* accordingly).
*/
void hmac_init ( struct digest_algorithm *digest, void *digest_ctx,
void *key, size_t *key_len ) {
unsigned char k_ipad[digest->blocksize];
void hmac_init ( struct digest_algorithm *digest, void *ctx, const void *key,
size_t key_len ) {
hmac_context_t ( digest ) *hctx = ctx;
unsigned int i;
/* Reduce key if necessary */
if ( *key_len > sizeof ( k_ipad ) )
hmac_reduce_key ( digest, key, key_len );
/* Construct input pad */
memset ( k_ipad, 0, sizeof ( k_ipad ) );
memcpy ( k_ipad, key, *key_len );
for ( i = 0 ; i < sizeof ( k_ipad ) ; i++ ) {
k_ipad[i] ^= 0x36;
memset ( hctx->pad, 0, sizeof ( hctx->pad ) );
if ( key_len <= sizeof ( hctx->pad ) ) {
memcpy ( hctx->pad, key, key_len );
} else {
digest_init ( digest, hctx->ctx );
digest_update ( digest, hctx->ctx, key, key_len );
digest_final ( digest, hctx->ctx, hctx->pad );
}
for ( i = 0 ; i < sizeof ( hctx->pad ) ; i++ ) {
hctx->pad[i] ^= 0x36;
}
/* Start inner hash */
digest_init ( digest, digest_ctx );
digest_update ( digest, digest_ctx, k_ipad, sizeof ( k_ipad ) );
digest_init ( digest, hctx->ctx );
digest_update ( digest, hctx->ctx, hctx->pad, sizeof ( hctx->pad ) );
}
/**
* Finalise HMAC
*
* @v digest Digest algorithm to use
* @v digest_ctx Digest context
* @v key Key
* @v key_len Length of key
* @v ctx HMAC context
* @v hmac HMAC digest to fill in
*
* The length of the key should be less than the block size of the
* digest algorithm being used. (If the key length is greater, it
* will be replaced with its own digest, and key_len will be updated
* accordingly).
*/
void hmac_final ( struct digest_algorithm *digest, void *digest_ctx,
void *key, size_t *key_len, void *hmac ) {
unsigned char k_opad[digest->blocksize];
void hmac_final ( struct digest_algorithm *digest, void *ctx, void *hmac ) {
hmac_context_t ( digest ) *hctx = ctx;
unsigned int i;
/* Reduce key if necessary */
if ( *key_len > sizeof ( k_opad ) )
hmac_reduce_key ( digest, key, key_len );
/* Construct output pad */
memset ( k_opad, 0, sizeof ( k_opad ) );
memcpy ( k_opad, key, *key_len );
for ( i = 0 ; i < sizeof ( k_opad ) ; i++ ) {
k_opad[i] ^= 0x5c;
/* Construct output pad from input pad */
for ( i = 0 ; i < sizeof ( hctx->pad ) ; i++ ) {
hctx->pad[i] ^= 0x6a;
}
/* Finish inner hash */
digest_final ( digest, digest_ctx, hmac );
digest_final ( digest, hctx->ctx, hmac );
/* Perform outer hash */
digest_init ( digest, digest_ctx );
digest_update ( digest, digest_ctx, k_opad, sizeof ( k_opad ) );
digest_update ( digest, digest_ctx, hmac, digest->digestsize );
digest_final ( digest, digest_ctx, hmac );
digest_init ( digest, hctx->ctx );
digest_update ( digest, hctx->ctx, hctx->pad, sizeof ( hctx->pad ) );
digest_update ( digest, hctx->ctx, hmac, digest->digestsize );
digest_final ( digest, hctx->ctx, hmac );
/* Erase output pad (from which the key may be derivable) */
memset ( hctx->pad, 0, sizeof ( hctx->pad ) );
}