diff --git a/ChangeLog b/ChangeLog index 1257e6133..ef245367a 100644 --- a/ChangeLog +++ b/ChangeLog @@ -9,6 +9,9 @@ Changes Security * Removed further timing differences during SSL message decryption in ssl_decrypt_buf() + * Removed timing differences due to bad padding from + rsa_rsaes_pkcs1_v15_decrypt() and rsa_pkcs1_decrypt() for PKCS#1 v1.5 + operations = Version 1.1.5 released on 2013-01-16 Bugfix diff --git a/library/rsa.c b/library/rsa.c index 614b23c84..673614ea5 100644 --- a/library/rsa.c +++ b/library/rsa.c @@ -484,9 +484,9 @@ int rsa_pkcs1_decrypt( rsa_context *ctx, unsigned char *output, size_t output_max_len) { - int ret; - size_t ilen; - unsigned char *p; + int ret, correct = 1; + size_t ilen, pad_count = 0; + unsigned char *p, *q; unsigned char bt; unsigned char buf[1024]; #if defined(POLARSSL_PKCS1_V21) @@ -515,36 +515,57 @@ int rsa_pkcs1_decrypt( rsa_context *ctx, case RSA_PKCS_V15: if( *p++ != 0 ) - return( POLARSSL_ERR_RSA_INVALID_PADDING ); + correct = 0; bt = *p++; if( ( bt != RSA_CRYPT && mode == RSA_PRIVATE ) || ( bt != RSA_SIGN && mode == RSA_PUBLIC ) ) { - return( POLARSSL_ERR_RSA_INVALID_PADDING ); + correct = 0; } if( bt == RSA_CRYPT ) { while( *p != 0 && p < buf + ilen - 1 ) - p++; + pad_count += ( *p++ != 0 ); - if( *p != 0 || p >= buf + ilen - 1 ) - return( POLARSSL_ERR_RSA_INVALID_PADDING ); + correct &= ( *p == 0 && p < buf + ilen - 1 ); + q = p; + + // Also pass over all other bytes to reduce timing differences + // + while ( q < buf + ilen - 1 ) + pad_count += ( *q++ != 0 ); + + // Prevent compiler optimization of pad_count + // + correct |= pad_count & 0x100000; /* Always 0 unless 1M bit keys */ p++; } else { while( *p == 0xFF && p < buf + ilen - 1 ) - p++; + pad_count += ( *p++ == 0xFF ); - if( *p != 0 || p >= buf + ilen - 1 ) - return( POLARSSL_ERR_RSA_INVALID_PADDING ); + correct &= ( *p == 0 && p < buf + ilen - 1 ); + q = p; + + // Also pass over all other bytes to reduce timing differences + // + while ( q < buf + ilen - 1 ) + pad_count += ( *q++ != 0 ); + + // Prevent compiler optimization of pad_count + // + correct |= pad_count & 0x100000; /* Always 0 unless 1M bit keys */ p++; } + if( correct == 0 ) + return( POLARSSL_ERR_RSA_INVALID_PADDING ); + break; #if defined(POLARSSL_PKCS1_V21)