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Backport 2.16: Fix GCM calculation with very long IV #5135

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Nov 22, 2021
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Backport 2.16: Fix GCM calculation with very long IV #5135

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3 changes: 3 additions & 0 deletions ChangeLog.d/bugfix-for-gcm-long-iv-size.txt
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Original file line number Diff line number Diff line change
@@ -0,0 +1,3 @@
Bugfix
* Fix a bug in mbedtls_gcm_starts() when bits of iv are longer than 2^32.
* Fix #4884.
18 changes: 17 additions & 1 deletion library/gcm.c
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Original file line number Diff line number Diff line change
Expand Up @@ -111,6 +111,20 @@
}
#endif

#ifndef PUT_UINT64_BE
#define PUT_UINT64_BE( n, b, i ) \
{ \
( b )[( i ) ] = (unsigned char) ( ( (n) >> 56 ) & 0xff ); \
( b )[( i ) + 1] = (unsigned char) ( ( (n) >> 48 ) & 0xff ); \
( b )[( i ) + 2] = (unsigned char) ( ( (n) >> 40 ) & 0xff ); \
( b )[( i ) + 3] = (unsigned char) ( ( (n) >> 32 ) & 0xff ); \
( b )[( i ) + 4] = (unsigned char) ( ( (n) >> 24 ) & 0xff ); \
( b )[( i ) + 5] = (unsigned char) ( ( (n) >> 16 ) & 0xff ); \
( b )[( i ) + 6] = (unsigned char) ( ( (n) >> 8 ) & 0xff ); \
( b )[( i ) + 7] = (unsigned char) ( ( (n) ) & 0xff ); \
}
#endif

/*
* Initialize a context
*/
Expand Down Expand Up @@ -309,6 +323,7 @@ int mbedtls_gcm_starts( mbedtls_gcm_context *ctx,
size_t i;
const unsigned char *p;
size_t use_len, olen = 0;
uint64_t iv_bits;

GCM_VALIDATE_RET( ctx != NULL );
GCM_VALIDATE_RET( iv != NULL );
Expand Down Expand Up @@ -338,7 +353,8 @@ int mbedtls_gcm_starts( mbedtls_gcm_context *ctx,
else
{
memset( work_buf, 0x00, 16 );
PUT_UINT32_BE( iv_len * 8, work_buf, 12 );
iv_bits = (uint64_t)iv_len * 8;
PUT_UINT64_BE( iv_bits, work_buf, 8 );

p = iv;
while( iv_len > 0 )
Expand Down