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Add pointers to in/out CID fields to mbedtls_ssl_context

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mbedtls_ssl_context contains pointers in_buf, in_hdr, in_len, ...
which point to various parts of the header of an incoming TLS or
DTLS record; similarly, there are pointers out_buf, ... for
outgoing records.

This commit adds fields in_cid and out_cid which point to where
the CID of incoming/outgoing records should reside, if present,
namely prior to where the record length resides.

Quoting https://tools.ietf.org/html/draft-ietf-tls-dtls-connection-id-04:

   The DTLSInnerPlaintext value is then encrypted and the CID added to
   produce the final DTLSCiphertext.

        struct {
            ContentType special_type = tls12_cid; /* 25 */
            ProtocolVersion version;
            uint16 epoch;
            uint48 sequence_number;
            opaque cid[cid_length];               // New field
            uint16 length;
            opaque enc_content[DTLSCiphertext.length];
        } DTLSCiphertext;

For outgoing records, out_cid is set in ssl_update_out_pointers()
based on the settings in the current outgoing transform.

For incoming records, ssl_update_in_pointers() sets in_cid as if no
CID was present, and it is the responsibility of ssl_parse_record_header()
to update the field (as well as in_len, in_msg and in_iv) when parsing
records that do contain a CID. This will be done in a subsequent commit.

Finally, the code around the invocations of ssl_decrypt_buf()
and ssl_encrypt_buf() is adapted to transfer the CID from the
input/output buffer to the CID field in the internal record
structure (which is what ssl_{encrypt/decrypt}_buf() uses).

Note that mbedtls_ssl_in_hdr_len() doesn't need change because
it infers the header length as in_iv - in_hdr, which will account
for the CID for records using such.
This commit is contained in:
Hanno Becker 2019-05-03 14:34:53 +01:00
parent 6cbad5560d
commit f9c6a4bea1
2 changed files with 35 additions and 4 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

8
include/mbedtls/ssl.h
View file

@ -1182,6 +1182,10 @@ struct mbedtls_ssl_context
TLS: maintained by us
DTLS: read from peer */
unsigned char *in_hdr; /*!< start of record header */
#if defined(MBEDTLS_SSL_CID)
unsigned char *in_cid; /*!< The start of the CID;
* (the end is marked by in_len). */
#endif /* MBEDTLS_SSL_CID */
unsigned char *in_len; /*!< two-bytes message length field */
unsigned char *in_iv; /*!< ivlen-byte IV */
unsigned char *in_msg; /*!< message contents (in_iv+ivlen) */
@ -1218,6 +1222,10 @@ struct mbedtls_ssl_context
unsigned char *out_buf; /*!< output buffer */
unsigned char *out_ctr; /*!< 64-bit outgoing message counter */
unsigned char *out_hdr; /*!< start of record header */
#if defined(MBEDTLS_SSL_CID)
unsigned char *out_cid; /*!< The start of the CID;
* (the end is marked by in_len). */
#endif /* MBEDTLS_SSL_CID */
unsigned char *out_len; /*!< two-bytes message length field */
unsigned char *out_iv; /*!< ivlen-byte IV */
unsigned char *out_msg; /*!< message contents (out_iv+ivlen) */

31
library/ssl_tls.c
View file

@ -4177,6 +4177,9 @@ int mbedtls_ssl_write_record( mbedtls_ssl_context *ssl, uint8_t force_flush )
return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
}
#if defined(MBEDTLS_SSL_CID )
memcpy( ssl->out_cid, rec.cid, rec.cid_len );
#endif /* MBEDTLS_SSL_CID */
ssl->out_msglen = len = rec.data_len;
ssl->out_len[0] = (unsigned char)( rec.data_len >> 8 );
ssl->out_len[1] = (unsigned char)( rec.data_len );
@ -5037,6 +5040,10 @@ static int ssl_prepare_record_content( mbedtls_ssl_context *ssl )
- ( ssl->in_iv - ssl->in_buf );
rec.data_len = ssl->in_msglen;
rec.data_offset = 0;
#if defined(MBEDTLS_SSL_CID )
rec.cid_len = ssl->in_len - ssl->in_cid;
memcpy( rec.cid, ssl->in_cid, rec.cid_len );
#endif /* MBEDTLS_SSL_CID */
memcpy( &rec.ctr[0], ssl->in_ctr, 8 );
mbedtls_ssl_write_version( ssl->major_ver, ssl->minor_ver,
@ -7980,8 +7987,15 @@ static void ssl_update_out_pointers( mbedtls_ssl_context *ssl,
if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM )
{
ssl->out_ctr = ssl->out_hdr + 3;
ssl->out_len = ssl->out_hdr + 11;
ssl->out_iv = ssl->out_hdr + 13;
#if defined(MBEDTLS_SSL_CID)
ssl->out_cid = ssl->out_ctr + 8;
ssl->out_len = ssl->out_cid;
if( transform != NULL )
ssl->out_len += transform->out_cid_len;
#else /* MBEDTLS_SSL_CID */
ssl->out_len = ssl->out_ctr + 8;
#endif /* MBEDTLS_SSL_CID */
ssl->out_iv = ssl->out_len + 2;
}
else
#endif
@ -8024,9 +8038,18 @@ static void ssl_update_in_pointers( mbedtls_ssl_context *ssl )
#if defined(MBEDTLS_SSL_PROTO_DTLS)
if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM )
{
/* This sets the header pointers to match records
* without CID. When we receive a record containing
* a CID, the fields are shifted accordingly in
* ssl_parse_record_header(). */
ssl->in_ctr = ssl->in_hdr + 3;
ssl->in_len = ssl->in_hdr + 11;
ssl->in_iv = ssl->in_hdr + 13;
#if defined(MBEDTLS_SSL_CID)
ssl->in_cid = ssl->in_ctr + 8;
ssl->in_len = ssl->in_cid; /* Default: no CID */
#else /* MBEDTLS_SSL_CID */
ssl->in_len = ssl->in_ctr + 8;
#endif /* MBEDTLS_SSL_CID */
ssl->in_iv = ssl->in_len + 2;
}
else
#endif