}
+/** Determines SRTP Roll-Over-Counter (in host-byte order) */
+static uint32_t
+srtp_compute_roc (const srtp_session_t *s, uint16_t seq)
+{
+ uint32_t roc = s->rtp_roc;
+
+ if (((seq - s->rtp_seq) & 0xffff) < 0x8000)
+ {
+ /* Sequence is ahead, good */
+ if (seq < s->rtp_seq)
+ roc++; /* Sequence number wrap */
+ }
+ else
+ {
+ /* Sequence is late, bad */
+ if (seq > s->rtp_seq)
+ roc--; /* Wrap back */
+ }
+ return roc;
+}
+
+
+/** Returns RTP sequence (in host-byte order) */
+static inline uint16_t rtp_seq (const uint8_t *buf)
+{
+ return (buf[2] << 8) | buf[3];
+}
+
+
/** Message Authentication and Integrity for RTP */
static const uint8_t *
-rtp_digest (gcry_md_hd_t md, const void *data, size_t len, uint32_t roc)
+rtp_digest (srtp_session_t *s, const uint8_t *data, size_t len)
{
+ const gcry_md_hd_t md = s->rtp.mac;
+ uint32_t roc = htonl (srtp_compute_roc (s, rtp_seq (data)));
+
gcry_md_reset (md);
gcry_md_write (md, data, len);
- gcry_md_write (md, &(uint32_t){ htonl (roc) }, 4);
+ gcry_md_write (md, &roc, 4);
return gcry_md_read (md, 0);
}
return EINVAL;
/* Determines RTP 48-bits counter and SSRC */
- uint32_t ssrc;
+ uint16_t seq = rtp_seq (buf);
+ uint32_t roc = srtp_compute_roc (s, seq), ssrc;
memcpy (&ssrc, buf + 8, 4);
- uint16_t seq = (buf[2] << 8) | buf[3];
- if (((seq - s->rtp_seq) & 0xffff) < 32768)
- {
- if (seq < s->rtp_seq)
- s->rtp_roc++; /* Sequence number wrap */
- }
+ /* Updates ROC and sequence (it's safe now) */
+ if (roc > s->rtp_roc)
+ s->rtp_seq = seq, s->rtp_roc = roc;
else
- {
- if (seq > s->rtp_seq)
- s->rtp_roc--;
- }
-
- s->rtp_seq = seq;
+ if (seq > s->rtp_seq)
+ s->rtp_seq = seq;
+ /* Encrypt/Decrypt */
if (s->flags & SRTP_UNENCRYPTED)
return 0;
- if (rtp_crypt (s->rtp.cipher, ssrc, s->rtp_roc, seq, s->rtp.salt,
+ if (rtp_crypt (s->rtp.cipher, ssrc, roc, seq, s->rtp.salt,
buf + offset, len - offset))
return EINVAL;
if (val)
return val;
- if (s->flags & SRTP_UNAUTHENTICATED)
- return 0;
-
- if (bufsize < (len + s->tag_len))
- return ENOSPC;
+ if (!(s->flags & SRTP_UNAUTHENTICATED))
+ {
+ if (bufsize < (len + s->tag_len))
+ return ENOSPC;
- const uint8_t *tag = rtp_digest (s->rtp.mac, buf, len, s->rtp_roc);
- memcpy (buf + len, tag, s->tag_len);
- *lenp = len + s->tag_len;
+ const uint8_t *tag = rtp_digest (s, buf, len);
+ memcpy (buf + len, tag, s->tag_len);
+ *lenp = len + s->tag_len;
+ }
return 0;
}
if (!(s->flags & SRTP_UNAUTHENTICATED))
{
- if (len < s->tag_len)
+ if (len < (12u + s->tag_len))
return EINVAL;
len -= s->tag_len;
- const uint8_t *tag = rtp_digest (s->rtp.mac, buf, len, s->rtp_roc);
+ const uint8_t *tag = rtp_digest (s, buf, len);
if (memcmp (buf + len, tag, s->tag_len))
return EACCES;