Changeset e5c071abd8c79d19f3f6e19f626540e241c36849

Timestamp:

03/10/07 19:06:47 (1 year ago)

Author:

Rémi Denis-Courmont <rem@videolan.org>

git-committer:

Rémi Denis-Courmont <rem@videolan.org> 1173550007 +0000

git-parent:

[62e11e95946388cc8d9ae585c5737ef7ad1e67b5]

git-author:

Rémi Denis-Courmont <rem@videolan.org> 1173550007 +0000

Message:

SRTCP support

Files:

• libs/srtp/srtp.c (modified) (13 diffs)
• libs/srtp/srtp.h (modified) (1 diff)
• libs/srtp/test-aes.c (modified) (1 diff)

libs/srtp/srtp.c

@@ -38 +38 @@
-/* TODO:
- * Useful stuff:
-
+e
- * - replay protection
- *
- * Requirements for conformance:
- * - suites with NULL cipher
- * - SRTCP
- *
- * Useless stuff (because nothing depends on it):
@@ -159 +155 @@
-
-/**
-
+
+
+
+
- *
- * @param name cipher-suite name
@@ -258 +257 @@
-}
-
-#include <stdio.h>
-
-static int
@@ -268 +266 @@
-        return -1;
-
-32_t cipherkey[4], authkey[5
+8_t keybuf[20
-    uint8_t label = rtcp ? SRTCP_CRYPT : SRTP_CRYPT;
-
-cipherkey
-cipherkey
-authkey
-authkey
-++
+keybuf
+keybuf
+keybuf
+keybuf
+
-        return -1;
-
-    debug (" cipher key: %08x%08x%08x%08x\n auth key: %08x%08x%08x%08x%08x\n",
-            ntohl (cipherkey[0]), ntohl (cipherkey[1]), ntohl (cipherkey[2]),
-            ntohl (cipherkey[3]), ntohl (authkey[0]), ntohl (authkey[1]),
-            ntohl (authkey[2]), ntohl (authkey[3]), ntohl (authkey[4]));
-
-    return 0;
@@ -330 +323 @@
-
-
-
-/**
- * Sets (or resets) the master key and master salt for a SRTP session.
@@ -351 +343 @@
-/** AES-CM encryption/decryption (ctr length = 16 bytes) */
-static int
-en
+ctr_
-{
-    const size_t ctrlen = 16;
@@ -383 +375 @@
-
-/** AES-CM for RTP (salt = 14 bytes + 2 nul bytes) */
-line in
-en
-  
+
+
+
-{
-    /* Determines cryptographic counter (IV) */
@@ -395 +387 @@
-
-    /* Encryption */
-en
+ctr_
-}
-
@@ -415 +407 @@
- * decryption function).
- *
-crypted/diges
+-/decryp
- * @param len RTP packet length
- *
@@ -468 +460 @@
-        return 0;
-
-en
-  
+
+
-        return EINVAL;
-
@@ -517 +509 @@
- *
- * @param buf RTP packet to be digested/decrypted
-
-S
+S
+
- *
- * @return 0 on success, in case of error:
@@ -528 +520 @@
-{
-    size_t len = *lenp;
+    /* FIXME: anti-replay */
-
-    if (!(s->flags & SRTP_UNAUTHENTICATED))
@@ -534 +527 @@
-            return EINVAL;
-        len -= s->tag_len;
-        *lenp = len;
-
-        const uint8_t *tag = rtp_digest (s->rtp.mac, buf, len, s->rtp_roc);
-        debug  (" Auth tag: %08x%08x%04x (wanted)\n"
-                " Auth tag: %08x%08x%04x (recv'd)\n",
-                ntohl (((uint32_t *)tag)[0]), ntohl (((uint32_t *)tag)[1]),
-                ntohs (((uint16_t *)tag)[4]),
-                ntohl (((uint32_t *)w)[0]), ntohl (((uint32_t *)w)[1]),
-                ntohs (((uint16_t *)w)[4]));
-        if (memcmp (buf + len, tag, s->tag_len))
-            return EACCES;
-
-
-/* FIXME: anti-replay */
+
+
+}
-
-    return srtp_crypt (s, buf, len);
-}
-
+
+/** AES-CM for RTCP (salt = 14 bytes + 2 nul bytes) */
+static int
+rtcp_crypt (gcry_cipher_hd_t hd, uint32_t ssrc, uint32_t index,
+            const uint32_t *salt, uint8_t *data, size_t len)
+{
+    return rtp_crypt (hd, ssrc, index >> 16, index & 0xffff, salt, data, len);
+}
+
+
+/** Message Authentication and Integrity for RTCP */
+static const uint8_t *
+rtcp_digest (gcry_md_hd_t md, const void *data, size_t len)
+{
+    gcry_md_reset (md);
+    gcry_md_write (md, data, len);
+    return gcry_md_read (md, 0);
+}
+
+
+/**
+ * Encrypts/decrypts a RTCP packet and updates SRTCP context
+ * (CTR block cypher mode of operation has identical encryption and
+ * decryption function).
+ *
+ * @param buf RTCP packet to be en-/decrypted
+ * @param len RTCP packet length
+ *
+ * @return 0 on success, in case of error:
+ *  EINVAL  malformatted RTCP packet
+ */
+static int srtcp_crypt (srtp_session_t *s, uint8_t *buf, size_t len)
+{
+    assert (s != NULL);
+
+    /* 8-bytes unencrypted header, and 4-bytes unencrypted footer */
+    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 */
+
+    if (s->flags & SRTCP_UNENCRYPTED)
+        return 0;
+
+    uint32_t ssrc;
+    memcpy (&ssrc, buf + 4, 4);
+
+    if (rtcp_crypt (s->rtcp.cipher, ssrc, index, s->rtp.salt,
+                    buf + 8, len - 8))
+        return EINVAL;
+    return 0;
+}
+
+
+/**
+ * Turns a RTCP packet into a SRTCP packet: encrypt it, then computes
+ * the authentication tag and appends it.
+ *
+ * @param buf RTCP packet to be encrypted/digested
+ * @param lenp pointer to the RTCP packet length on entry,
+ *             set to the SRTCP length on exit (undefined in case of error)
+ * @param bufsize size (bytes) of the packet buffer
+ *
+ * @return 0 on success, in case of error:
+ *  EINVAL  malformatted RTCP packet or internal error
+ *  ENOSPC  bufsize is too small (to add index and authentication tag)
+ */
+int
+srtcp_send (srtp_session_t *s, uint8_t *buf, size_t *lenp, size_t bufsize)
+{
+    size_t len = *lenp;
+    if (bufsize < (len + 4 + s->tag_len))
+        return ENOSPC;
+
+    uint32_t index = s->rtcp_index;
+    if ((s->flags & SRTCP_UNENCRYPTED) == 0)
+        index |= 0x80000000; /* Set Encrypted bit */
+    memcpy (buf + len, &(uint32_t){ htonl (index) }, 4);
+
+    int val = srtcp_crypt (s, buf, len);
+    if (val)
+        return val;
+
+    len += 4; /* Digest SRTCP index too */
+
+    const uint8_t *tag = rtcp_digest (s->rtp.mac, buf, len);
+    memcpy (buf + len, tag, s->tag_len);
+    *lenp = len + s->tag_len;
+    return 0;
+}
+
+
+/**
+ * Turns a SRTCP packet into a RTCP packet: authenticates the packet,
+ * then decrypts it.
+ *
+ * @param buf RTCP packet to be digested/decrypted
+ * @param lenp pointer to the SRTCP packet length on entry,
+ *             set to the RTCP length on exit (undefined in case of error)
+ *
+ * @return 0 on success, in case of error:
+ *  EINVAL  malformatted SRTCP packet
+ *  EACCES  authentication failed (spoofed packet or out-of-sync)
+ */
+int
+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 -= s->tag_len;
+
+    const uint8_t *tag = rtcp_digest (s->rtp.mac, buf, len);
+    if (memcmp (buf + len, tag, s->tag_len))
+         return EACCES;
+
+    len -= 4; /* Remove SRTCP index befor decryption */
+    *lenp = len;
+
+    return srtp_crypt (s, buf, len);
+}
+

libs/srtp/srtp.h

@@ -40 +40 @@
-                             uint16_t winsize);
-void srtp_destroy (srtp_session_t *s);
+int srtp_setkey (srtp_session_t *s, const void *key, size_t keylen,
+                 const void *salt, size_t saltlen);
+
-int srtp_send (srtp_session_t *s, uint8_t *buf, size_t *lenp, size_t maxsize);
-int srtp_recv (srtp_session_t *s, uint8_t *buf, size_t *lenp);
+int srtcp_send (srtp_session_t *s, uint8_t *buf, size_t *lenp, size_t maxsiz);
+int srtcp_recv (srtp_session_t *s, uint8_t *buf, size_t *lenp);
-
-int srtp_setkey (srtp_session_t *s, const void *key, size_t keylen,
-                 const void *salt, size_t saltlen);
-# ifdef __cplusplus
-}

libs/srtp/test-aes.c

@@ -118 +118 @@
-        fatal ("Cipher key error");
-
-en
+
-        fatal ("Encryption failure");
-    gcry_cipher_close (hd);