/* TODO:
* Useful stuff:
* - ROC profile thingy (multicast really needs this)
- * - replay protection
*
* Useless stuff (because nothing depends on it):
* - non-nul key derivation rate
uint32_t rtcp_index;
uint32_t rtp_roc;
uint16_t rtp_seq;
+ uint16_t rtp_rcc;
uint8_t tag_len;
};
SRTCP_SALT
};
+
#ifdef WIN32
# include <winsock2.h>
#else
* internal cryptographic counters; it is however of course feasible to open
* multiple simultaneous sessions with the same master key.
*
- * @param name cipher-suite name
- * @param kdr key derivation rate
+ * @param encr encryption algorithm number
+ * @param auth authentication algortihm number
+ * @param tag_len authentication tag byte length (NOT including RCC)
* @param flags OR'ed optional flags.
*
* @return NULL in case of error
*/
srtp_session_t *
-srtp_create (const char *name, unsigned flags, unsigned kdr)
+srtp_create (int encr, int auth, unsigned tag_len, int prf, unsigned flags)
{
- assert (name != NULL);
+ if ((flags & ~SRTP_FLAGS_MASK) || init_libgcrypt ())
+ return NULL;
- if (kdr != 0)
- return NULL; // FIXME: KDR not implemented yet
+ int cipher, md;
+ switch (encr)
+ {
+ case SRTP_ENCR_NULL:
+ cipher = GCRY_CIPHER_NONE;
+ break;
- uint8_t tag_len;
- int cipher = GCRY_CIPHER_AES, md = GCRY_MD_SHA1;
+ case SRTP_ENCR_AES_CM:
+ cipher = GCRY_CIPHER_AES;
+ break;
- if (strcmp (name, "AES_CM_128_HMAC_SHA1_80") == 0)
- tag_len = 10;
- else
- if (strcmp (name, "AES_CM_128_HMAC_SHA1_32") == 0)
- tag_len = 4;
- else
- // F8_128_HMAC_SHA1_80 is not implemented
+ default:
+ return NULL;
+ }
+
+ switch (auth)
+ {
+ case SRTP_AUTH_NULL:
+ md = GCRY_MD_NONE;
+ break;
+
+ case SRTP_AUTH_HMAC_SHA1:
+ md = GCRY_MD_SHA1;
+ break;
+
+ default:
+ return NULL;
+ }
+
+ if (tag_len > gcry_md_get_algo_dlen (auth))
return NULL;
- if ((flags & ~SRTP_FLAGS_MASK) || init_libgcrypt ())
+ if (prf != SRTP_PRF_AES_CM)
return NULL;
srtp_session_t *s = malloc (sizeof (*s));
memset (s, 0, sizeof (*s));
s->flags = flags;
- s->kdr = kdr;
s->tag_len = tag_len;
if (proto_create (&s->rtp, cipher, md) == 0)
}
+/**
+ * Sets Roll-over-Counter Carry (RCC) rate for the SRTP session. If not
+ * specified (through this function), the default rate of ONE is assumed
+ * (i.e. every RTP packets will carry the RoC). RCC rate is ignored if none
+ * of the RCC mode has been selected.
+ *
+ * The RCC mode is selected through one of these flags for srtp_create():
+ * SRTP_RCC_MODE1: integrity protection only for RoC carrying packets
+ * SRTP_RCC_MODE2: integrity protection for all packets
+ * SRTP_RCC_MODE3: no integrity protection
+ *
+ * RCC mode 3 is insecure. Compared to plain RTP, it provides confidentiality
+ * (through encryption) but is much more prone to DoS. It can only be used if
+ * anti-spoofing protection is provided by lower network layers (e.g. IPsec,
+ * or trusted routers and proper source address filtering).
+ *
+ * If RCC rate is 1, RCC mode 1 and 2 are functionally identical.
+ *
+ * @param rate RoC Carry rate (MUST NOT be zero)
+ */
+void srtp_setrcc_rate (srtp_session_t *s, uint16_t rate)
+{
+ assert (rate != 0);
+ s->rtp_rcc = rate;
+}
+
+
/** AES-CM encryption/decryption (ctr length = 16 bytes) */
static int
ctr_crypt (gcry_cipher_hd_t hd, uint32_t *ctr, uint8_t *data, size_t len)
*
* @return 0 on success, in case of error:
* EINVAL malformatted RTP packet
+ * EACCES replayed packet or out-of-window or sync lost
*/
static int srtp_crypt (srtp_session_t *s, uint8_t *buf, size_t len)
{
memcpy (&ssrc, buf + 8, 4);
/* Updates ROC and sequence (it's safe now) */
- if (roc > s->rtp_roc)
+ int16_t diff = seq - s->rtp_seq;
+ if (diff > 0)
+ {
+ /* Sequence in the future, good */
+ s->rtp.window = s->rtp.window << diff;
+ s->rtp.window |= 1;
s->rtp_seq = seq, s->rtp_roc = roc;
+ }
else
- if (seq > s->rtp_seq)
- s->rtp_seq = seq;
+ {
+ /* Sequence in the past/present, bad */
+ diff = -diff;
+ if ((diff >= 64) || ((s->rtp.window >> diff) & 1))
+ return EACCES; /* Replay attack */
+ s->rtp.window |= 1 << diff;
+ }
/* Encrypt/Decrypt */
if (s->flags & SRTP_UNENCRYPTED)
* @return 0 on success, in case of error:
* EINVAL malformatted RTP packet or internal error
* ENOSPC bufsize is too small (to add authentication tag)
+ * EACCES packet would trigger a replay error on receiver
*/
int
srtp_send (srtp_session_t *s, uint8_t *buf, size_t *lenp, size_t bufsize)
srtp_recv (srtp_session_t *s, uint8_t *buf, size_t *lenp)
{
size_t len = *lenp;
- /* FIXME: anti-replay */
if (!(s->flags & SRTP_UNAUTHENTICATED))
{
if ((len < 12) || ((buf[0] >> 6) != 2))
return EINVAL;
- uint32_t index = s->rtcp_index++;
- if (index == 0x7fffffff)
- s->rtcp_index = 0; /* 31-bit wrap */
+ uint32_t index;
+ memcpy (&index, buf + len, 4);
+ index = ntohl (index);
+ if (((index >> 31) != 0) != ((s->flags & SRTCP_UNENCRYPTED) == 0))
+ return EINVAL; // E-bit mismatch
+ index &= ~(1 << 31); // clear E-bit for counter
+
+ /* Updates SRTCP index (safe here) */
+ int32_t diff = index - s->rtcp_index;
+ if (diff > 0)
+ {
+ /* Packet in the future, good */
+ s->rtcp.window = s->rtcp.window << diff;
+ s->rtcp.window |= 1;
+ s->rtcp_index = index;
+ }
+ else
+ {
+ /* Packet in the past/present, bad */
+ diff = -diff;
+ if ((diff >= 64) || ((s->rtcp.window >> diff) & 1))
+ return EACCES; // replay attack!
+ s->rtp.window |= 1 << diff;
+ }
+
+ /* Crypts SRTCP */
if (s->flags & SRTCP_UNENCRYPTED)
return 0;
if (bufsize < (len + 4 + s->tag_len))
return ENOSPC;
- uint32_t index = s->rtcp_index;
+ uint32_t index = ++s->rtcp_index;
+ if (index >> 31)
+ s->rtcp_index = index = 0; /* 31-bit wrap */
+
if ((s->flags & SRTCP_UNENCRYPTED) == 0)
index |= 0x80000000; /* Set Encrypted bit */
memcpy (buf + len, &(uint32_t){ htonl (index) }, 4);
if (val)
return val;
- len += 4; /* Digest SRTCP index too */
+ len += 4; /* Digests SRTCP index too */
const uint8_t *tag = rtcp_digest (s->rtp.mac, buf, len);
memcpy (buf + len, tag, s->tag_len);
srtcp_recv (srtp_session_t *s, uint8_t *buf, size_t *lenp)
{
size_t len = *lenp;
- /* FIXME: anti-replay ?? */
if (len < (4u + s->tag_len))
return EINVAL;
len -= 4; /* Remove SRTCP index before decryption */
*lenp = len;
-
return srtp_crypt (s, buf, len);
}
projects / vlc / blobdiff