Make CBC decoding constant time. (fb0a59cc) · Commits · CYBER - Cyber Security / TS 103 523 MSP / TLMSP / TLMSP OpenSSL

crypto/evp/c_allc.c

+2 −0

Original line number	Diff line number	Diff line
		@@ -195,11 +195,13 @@ void OpenSSL_add_all_ciphers(void)
		EVP_add_cipher(EVP_aes_256_xts());
		EVP_add_cipher_alias(SN_aes_256_cbc,"AES256");
		EVP_add_cipher_alias(SN_aes_256_cbc,"aes256");
		#if 0 /* Disabled because of timing side-channel leaks. */
		#if !defined(OPENSSL_NO_SHA) && !defined(OPENSSL_NO_SHA1)
		EVP_add_cipher(EVP_aes_128_cbc_hmac_sha1());
		EVP_add_cipher(EVP_aes_256_cbc_hmac_sha1());
		#endif
		#endif
		#endif

		#ifndef OPENSSL_NO_CAMELLIA
		EVP_add_cipher(EVP_camellia_128_ecb());

ssl/Makefile

+2 −2

Original line number	Diff line number	Diff line
		@@ -22,7 +22,7 @@ LIB=$(TOP)/libssl.a
		SHARED_LIB= libssl$(SHLIB_EXT)
		LIBSRC= \
		s2_meth.c s2_srvr.c s2_clnt.c s2_lib.c s2_enc.c s2_pkt.c \
		s3_meth.c s3_srvr.c s3_clnt.c s3_lib.c s3_enc.c s3_pkt.c s3_both.c \
		s3_meth.c s3_srvr.c s3_clnt.c s3_lib.c s3_enc.c s3_pkt.c s3_both.c s3_cbc.c \
		s23_meth.c s23_srvr.c s23_clnt.c s23_lib.c s23_pkt.c \
		t1_meth.c t1_srvr.c t1_clnt.c t1_lib.c t1_enc.c \
		d1_meth.c d1_srvr.c d1_clnt.c d1_lib.c d1_pkt.c \
		@@ -33,7 +33,7 @@ LIBSRC= \
		bio_ssl.c ssl_err.c kssl.c t1_reneg.c tls_srp.c t1_trce.c
		LIBOBJ= \
		s2_meth.o s2_srvr.o s2_clnt.o s2_lib.o s2_enc.o s2_pkt.o \
		s3_meth.o s3_srvr.o s3_clnt.o s3_lib.o s3_enc.o s3_pkt.o s3_both.o \
		s3_meth.o s3_srvr.o s3_clnt.o s3_lib.o s3_enc.o s3_pkt.o s3_both.o s3_cbc.o \
		s23_meth.o s23_srvr.o s23_clnt.o s23_lib.o s23_pkt.o \
		t1_meth.o t1_srvr.o t1_clnt.o t1_lib.o t1_enc.o \
		d1_meth.o d1_srvr.o d1_clnt.o d1_lib.o d1_pkt.o \

ssl/d1_enc.c

+7 −42

Original line number	Diff line number	Diff line
		@@ -131,15 +131,15 @@ int dtls1_enc(SSL *s, int send)
		SSL3_RECORD *rec;
		EVP_CIPHER_CTX *ds;
		unsigned long l;
		int bs,i,ii,j,k,n=0;
		int bs,i,j,k,mac_size=0;
		const EVP_CIPHER *enc;

		if (send)
		{
		if (EVP_MD_CTX_md(s->write_hash))
		{
		n=EVP_MD_CTX_size(s->write_hash);
		if (n < 0)
		mac_size=EVP_MD_CTX_size(s->write_hash);
		if (mac_size < 0)
		return -1;
		}
		ds=s->enc_write_ctx;
		@@ -164,8 +164,8 @@ int dtls1_enc(SSL *s, int send)
		{
		if (EVP_MD_CTX_md(s->read_hash))
		{
		n=EVP_MD_CTX_size(s->read_hash);
		if (n < 0)
		mac_size=EVP_MD_CTX_size(s->read_hash);
		if (mac_size < 0)
		return -1;
		}
		ds=s->enc_read_ctx;
		@@ -245,44 +245,9 @@ int dtls1_enc(SSL *s, int send)
		}
		#endif /* KSSL_DEBUG */

		rec->orig_len = rec->length;
		if ((bs != 1) && !send)
		{
		ii=i=rec->data[l-1]; /* padding_length */
		i++;
		if (s->options&SSL_OP_TLS_BLOCK_PADDING_BUG)
		{
		/* First packet is even in size, so check */
		if ((memcmp(s->s3->read_sequence,
		"\0\0\0\0\0\0\0\0",8) == 0) && !(ii & 1))
		s->s3->flags\|=TLS1_FLAGS_TLS_PADDING_BUG;
		if (s->s3->flags & TLS1_FLAGS_TLS_PADDING_BUG)
		i--;
		}
		/* TLS 1.0 does not bound the number of padding bytes by the block size.
		* All of them must have value 'padding_length'. */
		if (i + bs > (int)rec->length)
		{
		/* Incorrect padding. SSLerr() and ssl3_alert are done
		* by caller: we don't want to reveal whether this is
		* a decryption error or a MAC verification failure
		* (see http://www.openssl.org/~bodo/tls-cbc.txt)
		*/
		return -1;
		}
		for (j=(int)(l-i); j<(int)l; j++)
		{
		if (rec->data[j] != ii)
		{
		/* Incorrect padding */
		return -1;
		}
		}
		rec->length-=i;

		rec->data += bs; /* skip the implicit IV */
		rec->input += bs;
		rec->length -= bs;
		}
		return tls1_cbc_remove_padding(s, rec, bs, mac_size);
		}
		return(1);
		}

ssl/s3_enc.c

+69 −39

Original line number	Diff line number	Diff line
		@@ -492,7 +492,7 @@ int ssl3_enc(SSL *s, int send)
		SSL3_RECORD *rec;
		EVP_CIPHER_CTX *ds;
		unsigned long l;
		int bs,i;
		int bs,i,mac_size=0;
		const EVP_CIPHER *enc;

		if (send)
		@@ -553,22 +553,12 @@ int ssl3_enc(SSL *s, int send)

		EVP_Cipher(ds,rec->data,rec->input,l);

		rec->orig_len = rec->length;

		if (EVP_MD_CTX_md(s->read_hash) != NULL)
		mac_size = EVP_MD_CTX_size(s->read_hash);
		if ((bs != 1) && !send)
		{
		i=rec->data[l-1]+1;
		/* SSL 3.0 bounds the number of padding bytes by the block size;
		* padding bytes (except the last one) are arbitrary */
		if (i > bs)
		{
		/* Incorrect padding. SSLerr() and ssl3_alert are done
		* by caller: we don't want to reveal whether this is
		* a decryption error or a MAC verification failure
		* (see http://www.openssl.org/~bodo/tls-cbc.txt) */
		return -1;
		}
		/* now i <= bs <= rec->length */
		rec->length-=i;
		}
		return ssl3_cbc_remove_padding(s, rec, bs, mac_size);
		}
		return(1);
		}
		@@ -737,7 +727,7 @@ int n_ssl3_mac(SSL ssl, unsigned char md, int send)
		EVP_MD_CTX md_ctx;
		const EVP_MD_CTX *hash;
		unsigned char *p,rec_char;
		unsigned int md_size;
		size_t md_size;
		int npad;
		int t;

		@@ -762,6 +752,44 @@ int n_ssl3_mac(SSL ssl, unsigned char md, int send)
		md_size=t;
		npad=(48/md_size)*md_size;

		if (!send &&
		EVP_CIPHER_CTX_mode(ssl->enc_read_ctx) == EVP_CIPH_CBC_MODE &&
		ssl3_cbc_record_digest_supported(hash))
		{
		/* This is a CBC-encrypted record. We must avoid leaking any
		* timing-side channel information about how many blocks of
		* data we are hashing because that gives an attacker a
		* timing-oracle. */

		/* npad is, at most, 48 bytes and that's with MD5:
		* 16 + 48 + 8 (sequence bytes) + 1 + 2 = 75.
		*
		* With SHA-1 (the largest hash speced for SSLv3) the hash size
		* goes up 4, but npad goes down by 8, resulting in a smaller
		* total size. */
		unsigned char header[75];
		unsigned j = 0;
		memcpy(header+j, mac_sec, md_size);
		j += md_size;
		memcpy(header+j, ssl3_pad_1, npad);
		j += npad;
		memcpy(header+j, seq, 8);
		j += 8;
		header[j++] = rec->type;
		header[j++] = rec->length >> 8;
		header[j++] = rec->length & 0xff;

		ssl3_cbc_digest_record(
		hash,
		md, &md_size,
		header, rec->input,
		rec->length + md_size, rec->orig_len,
		mac_sec, md_size,
		1 /* is SSLv3 */);
		}
		else
		{
		unsigned int md_size_u;
		/* Chop the digest off the end :-) */
		EVP_MD_CTX_init(&md_ctx);

		@@ -781,9 +809,11 @@ int n_ssl3_mac(SSL ssl, unsigned char md, int send)
		EVP_DigestUpdate(&md_ctx,mac_sec,md_size);
		EVP_DigestUpdate(&md_ctx,ssl3_pad_2,npad);
		EVP_DigestUpdate(&md_ctx,md,md_size);
		EVP_DigestFinal_ex( &md_ctx,md,&md_size);
		EVP_DigestFinal_ex( &md_ctx,md,&md_size_u);
		md_size = md_size_u;

		EVP_MD_CTX_cleanup(&md_ctx);
		}

		ssl3_record_sequence_update(seq);
		return(md_size);

ssl/s3_pkt.c

+38 −38

Original line number	Diff line number	Diff line
		@@ -290,11 +290,9 @@ static int ssl3_get_record(SSL *s)
		unsigned char *p;
		unsigned char md[EVP_MAX_MD_SIZE];
		short version;
		int mac_size;
		unsigned mac_size;
		int clear=0;
		size_t extra;
		int decryption_failed_or_bad_record_mac = 0;
		unsigned char *mac = NULL;

		rr= &(s->s3->rrec);
		sess=s->session;
		@@ -405,17 +403,10 @@ fprintf(stderr, "Record type=%d, Length=%d\n", rr->type, rr->length);
		rr->data=rr->input;

		enc_err = s->method->ssl3_enc->enc(s,0);
		if (enc_err <= 0)
		{
		if (enc_err == 0)
		{
		/* SSLerr() and ssl3_send_alert() have been called */
		goto err;

		/* Otherwise enc_err == -1, which indicates bad padding
		* (rec->length has not been changed in this case).
		* To minimize information leaked via timing, we will perform
		* the MAC computation anyway. */
		decryption_failed_or_bad_record_mac = 1;
		}

		#ifdef TLS_DEBUG
		@@ -433,45 +424,54 @@ printf("\n");
		if (!clear)
		{
		/* !clear => s->read_hash != NULL => mac_size != -1 */
		unsigned char *mac = NULL;
		unsigned char mac_tmp[EVP_MAX_MD_SIZE];
		mac_size=EVP_MD_CTX_size(s->read_hash);
		OPENSSL_assert(mac_size >= 0);
		OPENSSL_assert(mac_size <= EVP_MAX_MD_SIZE);

		if (rr->length > SSL3_RT_MAX_COMPRESSED_LENGTH+extra+mac_size)
		/* orig_len is the length of the record before any padding was
		* removed. This is public information, as is the MAC in use,
		* therefore we can safely process the record in a different
		* amount of time if it's too short to possibly contain a MAC.
		*/
		if (rr->orig_len < mac_size \|\|
		/* CBC records must have a padding length byte too. */
		(EVP_CIPHER_CTX_mode(s->enc_read_ctx) == EVP_CIPH_CBC_MODE &&
		rr->orig_len < mac_size+1))
		{
		#if 0 /* OK only for stream ciphers (then rr->length is visible from ciphertext anyway) */
		al=SSL_AD_RECORD_OVERFLOW;
		SSLerr(SSL_F_SSL3_GET_RECORD,SSL_R_PRE_MAC_LENGTH_TOO_LONG);
		al=SSL_AD_DECODE_ERROR;
		SSLerr(SSL_F_SSL3_GET_RECORD,SSL_R_LENGTH_TOO_SHORT);
		goto f_err;
		#else
		decryption_failed_or_bad_record_mac = 1;
		#endif
		}
		/* check the MAC for rr->input (it's in mac_size bytes at the tail) */
		if (rr->length >= (unsigned int)mac_size)

		if (EVP_CIPHER_CTX_mode(s->enc_read_ctx) == EVP_CIPH_CBC_MODE)
		{
		/* We update the length so that the TLS header bytes
		* can be constructed correctly but we need to extract
		* the MAC in constant time from within the record,
		* without leaking the contents of the padding bytes.
		* */
		mac = mac_tmp;
		ssl3_cbc_copy_mac(mac_tmp, rr, mac_size);
		rr->length -= mac_size;
		mac = &rr->data[rr->length];
		}
		else
		{
		/* record (minus padding) is too short to contain a MAC */
		#if 0 /* OK only for stream ciphers */
		al=SSL_AD_DECODE_ERROR;
		SSLerr(SSL_F_SSL3_GET_RECORD,SSL_R_LENGTH_TOO_SHORT);
		goto f_err;
		#else
		decryption_failed_or_bad_record_mac = 1;
		rr->length = 0;
		#endif
		/* In this case there's no padding, so \|rec->orig_len\|
		* equals \|rec->length\| and we checked that there's
		* enough bytes for \|mac_size\| above. */
		rr->length -= mac_size;
		mac = &rr->data[rr->length];
		}
		i=s->method->ssl3_enc->mac(s,md,0);

		i=s->method->ssl3_enc->mac(s,md,0 /* not send */);
		if (i < 0 \|\| mac == NULL \|\| CRYPTO_memcmp(md, mac, (size_t)mac_size) != 0)
		{
		decryption_failed_or_bad_record_mac = 1;
		}
		enc_err = -1;
		if (rr->length > SSL3_RT_MAX_COMPRESSED_LENGTH+extra+mac_size)
		enc_err = -1;
		}

		if (decryption_failed_or_bad_record_mac)
		if (enc_err < 0)
		{
		/* A separate 'decryption_failed' alert was introduced with TLS 1.0,
		* SSL 3.0 only has 'bad_record_mac'. But unless a decryption

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