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From 69675d056a7e335c0be907541aaab83de71ea8b5 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Manuel=20P=C3=A9gouri=C3=A9-Gonnard?=
<manuel.pegourie-gonnard@arm.com>
Date: Thu, 28 Jun 2018 12:10:27 +0200
Subject: [PATCH] Fix Lucky 13 cache attack on MD/SHA padding
The basis for the Lucky 13 family of attacks is for an attacker to be able to
distinguish between (long) valid TLS-CBC padding and invalid TLS-CBC padding.
Since our code sets padlen = 0 for invalid padding, the length of the input to
the HMAC function gives information about that.
Information about this length (modulo the MD/SHA block size) can be deduced
from how much MD/SHA padding (this is distinct from TLS-CBC padding) is used.
If MD/SHA padding is read from a (static) buffer, a local attacker could get
information about how much is used via a cache attack targeting that buffer.
Let's get rid of this buffer. Now the only buffer used is the internal MD/SHA
one, which is always read fully by the process() function.
[jcowgill: cherry picked from 2.1 branch]
[jcowgill: remove Changelog entry]
---
ChangeLog | 7 +++++++
library/md5.c | 49 ++++++++++++++++++++++++++++----------------
library/sha1.c | 49 ++++++++++++++++++++++++++++----------------
library/sha256.c | 49 ++++++++++++++++++++++++++++----------------
library/sha512.c | 53 +++++++++++++++++++++++++++++-------------------
5 files changed, 135 insertions(+), 72 deletions(-)
--- a/library/md5.c
+++ b/library/md5.c
@@ -275,36 +275,51 @@ void mbedtls_md5_update( mbedtls_md5_con
}
}
-static const unsigned char md5_padding[64] =
-{
- 0x80, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
- 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
- 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
- 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
-};
-
/*
* MD5 final digest
*/
void mbedtls_md5_finish( mbedtls_md5_context *ctx, unsigned char output[16] )
{
- uint32_t last, padn;
+ uint32_t used;
uint32_t high, low;
- unsigned char msglen[8];
+ /*
+ * Add padding: 0x80 then 0x00 until 8 bytes remain for the length
+ */
+ used = ctx->total[0] & 0x3F;
+
+ ctx->buffer[used++] = 0x80;
+
+ if( used <= 56 )
+ {
+ /* Enough room for padding + length in current block */
+ memset( ctx->buffer + used, 0, 56 - used );
+ }
+ else
+ {
+ /* We'll need an extra block */
+ memset( ctx->buffer + used, 0, 64 - used );
+
+ mbedtls_md5_process( ctx, ctx->buffer );
+
+ memset( ctx->buffer, 0, 56 );
+ }
+
+ /*
+ * Add message length
+ */
high = ( ctx->total[0] >> 29 )
| ( ctx->total[1] << 3 );
low = ( ctx->total[0] << 3 );
- PUT_UINT32_LE( low, msglen, 0 );
- PUT_UINT32_LE( high, msglen, 4 );
-
- last = ctx->total[0] & 0x3F;
- padn = ( last < 56 ) ? ( 56 - last ) : ( 120 - last );
+ PUT_UINT32_LE( low, ctx->buffer, 56 );
+ PUT_UINT32_LE( high, ctx->buffer, 60 );
- mbedtls_md5_update( ctx, md5_padding, padn );
- mbedtls_md5_update( ctx, msglen, 8 );
+ mbedtls_md5_process( ctx, ctx->buffer );
+ /*
+ * Output final state
+ */
PUT_UINT32_LE( ctx->state[0], output, 0 );
PUT_UINT32_LE( ctx->state[1], output, 4 );
PUT_UINT32_LE( ctx->state[2], output, 8 );
--- a/library/sha1.c
+++ b/library/sha1.c
@@ -307,36 +307,51 @@ void mbedtls_sha1_update( mbedtls_sha1_c
memcpy( (void *) (ctx->buffer + left), input, ilen );
}
-static const unsigned char sha1_padding[64] =
-{
- 0x80, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
- 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
- 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
- 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
-};
-
/*
* SHA-1 final digest
*/
void mbedtls_sha1_finish( mbedtls_sha1_context *ctx, unsigned char output[20] )
{
- uint32_t last, padn;
+ uint32_t used;
uint32_t high, low;
- unsigned char msglen[8];
+ /*
+ * Add padding: 0x80 then 0x00 until 8 bytes remain for the length
+ */
+ used = ctx->total[0] & 0x3F;
+
+ ctx->buffer[used++] = 0x80;
+
+ if( used <= 56 )
+ {
+ /* Enough room for padding + length in current block */
+ memset( ctx->buffer + used, 0, 56 - used );
+ }
+ else
+ {
+ /* We'll need an extra block */
+ memset( ctx->buffer + used, 0, 64 - used );
+
+ mbedtls_sha1_process( ctx, ctx->buffer );
+
+ memset( ctx->buffer, 0, 56 );
+ }
+
+ /*
+ * Add message length
+ */
high = ( ctx->total[0] >> 29 )
| ( ctx->total[1] << 3 );
low = ( ctx->total[0] << 3 );
- PUT_UINT32_BE( high, msglen, 0 );
- PUT_UINT32_BE( low, msglen, 4 );
-
- last = ctx->total[0] & 0x3F;
- padn = ( last < 56 ) ? ( 56 - last ) : ( 120 - last );
+ PUT_UINT32_BE( high, ctx->buffer, 56 );
+ PUT_UINT32_BE( low, ctx->buffer, 60 );
- mbedtls_sha1_update( ctx, sha1_padding, padn );
- mbedtls_sha1_update( ctx, msglen, 8 );
+ mbedtls_sha1_process( ctx, ctx->buffer );
+ /*
+ * Output final state
+ */
PUT_UINT32_BE( ctx->state[0], output, 0 );
PUT_UINT32_BE( ctx->state[1], output, 4 );
PUT_UINT32_BE( ctx->state[2], output, 8 );
--- a/library/sha256.c
+++ b/library/sha256.c
@@ -276,36 +276,51 @@ void mbedtls_sha256_update( mbedtls_sha2
memcpy( (void *) (ctx->buffer + left), input, ilen );
}
-static const unsigned char sha256_padding[64] =
-{
- 0x80, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
- 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
- 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
- 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
-};
-
/*
* SHA-256 final digest
*/
void mbedtls_sha256_finish( mbedtls_sha256_context *ctx, unsigned char output[32] )
{
- uint32_t last, padn;
+ uint32_t used;
uint32_t high, low;
- unsigned char msglen[8];
+ /*
+ * Add padding: 0x80 then 0x00 until 8 bytes remain for the length
+ */
+ used = ctx->total[0] & 0x3F;
+
+ ctx->buffer[used++] = 0x80;
+
+ if( used <= 56 )
+ {
+ /* Enough room for padding + length in current block */
+ memset( ctx->buffer + used, 0, 56 - used );
+ }
+ else
+ {
+ /* We'll need an extra block */
+ memset( ctx->buffer + used, 0, 64 - used );
+
+ mbedtls_sha256_process( ctx, ctx->buffer );
+
+ memset( ctx->buffer, 0, 56 );
+ }
+
+ /*
+ * Add message length
+ */
high = ( ctx->total[0] >> 29 )
| ( ctx->total[1] << 3 );
low = ( ctx->total[0] << 3 );
- PUT_UINT32_BE( high, msglen, 0 );
- PUT_UINT32_BE( low, msglen, 4 );
-
- last = ctx->total[0] & 0x3F;
- padn = ( last < 56 ) ? ( 56 - last ) : ( 120 - last );
+ PUT_UINT32_BE( high, ctx->buffer, 56 );
+ PUT_UINT32_BE( low, ctx->buffer, 60 );
- mbedtls_sha256_update( ctx, sha256_padding, padn );
- mbedtls_sha256_update( ctx, msglen, 8 );
+ mbedtls_sha256_process( ctx, ctx->buffer );
+ /*
+ * Output final state
+ */
PUT_UINT32_BE( ctx->state[0], output, 0 );
PUT_UINT32_BE( ctx->state[1], output, 4 );
PUT_UINT32_BE( ctx->state[2], output, 8 );
--- a/library/sha512.c
+++ b/library/sha512.c
@@ -306,40 +306,51 @@ void mbedtls_sha512_update( mbedtls_sha5
memcpy( (void *) (ctx->buffer + left), input, ilen );
}
-static const unsigned char sha512_padding[128] =
-{
- 0x80, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
- 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
- 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
- 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
- 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
- 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
- 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
- 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
-};
-
/*
* SHA-512 final digest
*/
void mbedtls_sha512_finish( mbedtls_sha512_context *ctx, unsigned char output[64] )
{
- size_t last, padn;
+ unsigned used;
uint64_t high, low;
- unsigned char msglen[16];
+ /*
+ * Add padding: 0x80 then 0x00 until 16 bytes remain for the length
+ */
+ used = ctx->total[0] & 0x7F;
+
+ ctx->buffer[used++] = 0x80;
+
+ if( used <= 112 )
+ {
+ /* Enough room for padding + length in current block */
+ memset( ctx->buffer + used, 0, 112 - used );
+ }
+ else
+ {
+ /* We'll need an extra block */
+ memset( ctx->buffer + used, 0, 128 - used );
+
+ mbedtls_sha512_process( ctx, ctx->buffer );
+
+ memset( ctx->buffer, 0, 112 );
+ }
+
+ /*
+ * Add message length
+ */
high = ( ctx->total[0] >> 61 )
| ( ctx->total[1] << 3 );
low = ( ctx->total[0] << 3 );
- PUT_UINT64_BE( high, msglen, 0 );
- PUT_UINT64_BE( low, msglen, 8 );
-
- last = (size_t)( ctx->total[0] & 0x7F );
- padn = ( last < 112 ) ? ( 112 - last ) : ( 240 - last );
+ PUT_UINT64_BE( high, ctx->buffer, 112 );
+ PUT_UINT64_BE( low, ctx->buffer, 120 );
- mbedtls_sha512_update( ctx, sha512_padding, padn );
- mbedtls_sha512_update( ctx, msglen, 16 );
+ mbedtls_sha512_process( ctx, ctx->buffer );
+ /*
+ * Output final state
+ */
PUT_UINT64_BE( ctx->state[0], output, 0 );
PUT_UINT64_BE( ctx->state[1], output, 8 );
PUT_UINT64_BE( ctx->state[2], output, 16 );
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