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Compute outgoing MAC in temporary buffer for MAC-then-Encrypt

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A previous commit changed the record encryption function
`ssl_encrypt_buf` to compute the MAC in a temporary buffer
and copying the relevant part of it (which is strictly smaller
if the truncated HMAC extension is used) to the outgoing message
buffer. However, the change was only made in case Encrypt-Then-MAC
was enabled, but not in case of MAC-Then-Encrypt. While this
doesn't constitute a problem, for the sake of uniformity this
commit changes `ssl_encrypt_buf` to compute the MAC in a temporary
buffer in this case, too.
This commit is contained in:
Hanno Becker 2018-01-05 16:24:22 +00:00
parent 47331a72e2
commit 394767c184
1 changed files with 6 additions and 2 deletions
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8
library/ssl_tls.c
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@ -1521,6 +1521,8 @@ static int ssl_encrypt_buf( mbedtls_ssl_context *ssl )
#if defined(MBEDTLS_SSL_ENCRYPT_THEN_MAC)
if( auth_done == 0 )
{
unsigned char mac[MBEDTLS_SSL_MAC_ADD];
/*
* MAC(MAC_write_key, seq_num +
* TLSCipherText.type +
@ -1543,10 +1545,12 @@ static int ssl_encrypt_buf( mbedtls_ssl_context *ssl )
mbedtls_md_hmac_update( &ssl->transform_out->md_ctx_enc, pseudo_hdr, 13 );
mbedtls_md_hmac_update( &ssl->transform_out->md_ctx_enc,
ssl->out_iv, ssl->out_msglen );
mbedtls_md_hmac_finish( &ssl->transform_out->md_ctx_enc,
ssl->out_iv + ssl->out_msglen );
mbedtls_md_hmac_finish( &ssl->transform_out->md_ctx_enc, mac );
mbedtls_md_hmac_reset( &ssl->transform_out->md_ctx_enc );
memcpy( ssl->out_iv + ssl->out_msglen, mac,
ssl->transform_out->maclen );
ssl->out_msglen += ssl->transform_out->maclen;
auth_done++;
}