Implement the per ssrc key derivation algorithm and add computed test vectors

.github/workflows/ghpages.yml

@@ -20,7 +20,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - name: "Checkout"
-      uses: actions/checkout@v2
+      uses: actions/checkout@v6
 
     - name: "Cache Setup"
       id: cache-setup
@@ -30,7 +30,7 @@ jobs:
         date -u "+::set-output name=date::%FT%T"
 
     - name: "Cache References"
-      uses: actions/cache@v2
+      uses: actions/cache@v4
       with:
         path: |
           ${{ steps.cache-setup.outputs.path }}
@@ -53,7 +53,7 @@ jobs:
         token: ${{ github.token }}
 
     - name: "Archive Built Drafts"
-      uses: actions/upload-artifact@v2
+      uses: actions/upload-artifact@v6
       with:
         path: |
           draft-*.html

reference-implementation/src/lib.rs

@@ -36,9 +36,13 @@ pub mod header;
 /// Cipher agility layer
 pub mod cipher;
 
+/// Per-SSRC stream key derivation for RTP
+pub mod per_ssrc_key_derivation;
+
 pub use crate::{
     cipher::{new_cipher, Cipher, CipherSuite, SFrameIntermediateValues},
     header::{Counter, Header, KeyId},
+    per_ssrc_key_derivation::derive_ssrc_key,
 };
 use std::collections::HashMap;
 

reference-implementation/src/per_ssrc_key_derivation.rs

@@ -0,0 +1,38 @@
+use hkdf::Hkdf;
+use hmac::SimpleHmac;
+use sha2::{Sha256, Sha512};
+
+/// Derive the per-SSRC stream key for a given SFrame cipher suite as defined in Section 7 of draft-ietf-avtcore-rtp-sframe
+///
+/// This implements the RTP stream key derivation from the SFrame RTP payload format draft:
+/// ```text
+/// PRK          = HKDF-Extract(salt=SSRC_big_endian_4_bytes, ikm=base_key)
+/// stream_key   = HKDF-Expand(PRK, info="SFrame 1.0 RTP Stream", L=Nh)
+/// ```
+///
+/// Hash function and output length (Nh) are determined by cipher suite:
+/// - Suites 0x0001–0x0004: SHA-256, Nh = 32
+/// - Suites 0x0005–0x0008: SHA-512, Nh = 64
+///
+/// # Panics
+/// Panics if `cipher_suite` is not in the range 0x0001–0x0008.
+pub fn derive_ssrc_key(ssrc: u32, base_key: &[u8], cipher_suite: u16) -> Vec<u8> {
+    static INFO: &[u8] = b"SFrame 1.0 RTP Stream";
+    let ssrc_salt = ssrc.to_be_bytes();
+
+    match cipher_suite {
+        0x0001..=0x0004 => {
+            let (_, h) = Hkdf::<Sha256>::extract(Some(&ssrc_salt), base_key);
+            let mut key = vec![0u8; 32];
+            h.expand(INFO, &mut key).expect("HKDF-Expand failed");
+            key
+        }
+        0x0005..=0x0008 => {
+            let (_, h) = Hkdf::<Sha512, SimpleHmac<Sha512>>::extract(Some(&ssrc_salt), base_key);
+            let mut key = vec![0u8; 64];
+            h.expand(INFO, &mut key).expect("HKDF-Expand failed");
+            key
+        }
+        _ => panic!("Unsupported SFrame cipher suite: 0x{:04x}", cipher_suite),
+    }
+}

reference-implementation/tests/per_ssrc_key_derivation.rs

@@ -0,0 +1,57 @@
+// Test harness for SFrame per-SSRC stream key derivation vectors.
+// Loads per-ssrc-key-derivation.json from the project's test-vectors directory
+// and verifies that the Rust implementation produces identical keys.
+
+use serde::Deserialize;
+use sframe_reference::derive_ssrc_key;
+
+#[derive(Deserialize)]
+struct VectorEntry {
+    cipher_suite: u16,
+    base_key: String,
+    ssrc_a: String,
+    ssrc_b: String,
+    stream_key_a: String,
+    stream_key_b: String,
+}
+
+fn hex_to_bytes(s: &str) -> Vec<u8> {
+    (0..s.len())
+        .step_by(2)
+        .map(|i| u8::from_str_radix(&s[i..i + 2], 16).expect("invalid hex"))
+        .collect()
+}
+
+fn parse_ssrc(s: &str) -> u32 {
+    u32::from_str_radix(s.trim_start_matches("0x"), 16).expect("invalid ssrc")
+}
+
+#[test]
+fn per_ssrc_stream_key_vectors() {
+    let json = include_str!("../../test-vectors/test-vectors-per-ssrc-key-derivation.json");
+    let entries: Vec<VectorEntry> = serde_json::from_str(json).expect("failed to parse vectors");
+
+    assert!(!entries.is_empty(), "Expected at least one vector entry");
+
+    for entry in &entries {
+        let base_key = hex_to_bytes(&entry.base_key);
+        let ssrc_a = parse_ssrc(&entry.ssrc_a);
+        let ssrc_b = parse_ssrc(&entry.ssrc_b);
+
+        let computed_a = derive_ssrc_key(ssrc_a, &base_key, entry.cipher_suite);
+        let computed_b = derive_ssrc_key(ssrc_b, &base_key, entry.cipher_suite);
+
+        assert_eq!(
+            computed_a,
+            hex_to_bytes(&entry.stream_key_a),
+            "stream_key_a mismatch for cipher_suite 0x{:04x}",
+            entry.cipher_suite
+        );
+        assert_eq!(
+            computed_b,
+            hex_to_bytes(&entry.stream_key_b),
+            "stream_key_b mismatch for cipher_suite 0x{:04x}",
+            entry.cipher_suite
+        );
+    }
+}

test-vectors/test-vectors-per-ssrc-key-derivation.json

@@ -0,0 +1,66 @@
+[
+  {
+    "cipher_suite": 1,
+    "base_key": "000102030405060708090a0b0c0d0e0f",
+    "ssrc_a": "0x12345678",
+    "ssrc_b": "0x98765432",
+    "stream_key_a": "f309f118aecdacfbc165cc080022b297100bbb55e483b002d762000a0faa684d",
+    "stream_key_b": "06e5d1b8c6e01f10b592bd2e13ff4b37182b895ec8330d5cc6ec690704043b5f"
+  },
+  {
+    "cipher_suite": 2,
+    "base_key": "000102030405060708090a0b0c0d0e0f",
+    "ssrc_a": "0x12345678",
+    "ssrc_b": "0x98765432",
+    "stream_key_a": "f309f118aecdacfbc165cc080022b297100bbb55e483b002d762000a0faa684d",
+    "stream_key_b": "06e5d1b8c6e01f10b592bd2e13ff4b37182b895ec8330d5cc6ec690704043b5f"
+  },
+  {
+    "cipher_suite": 3,
+    "base_key": "000102030405060708090a0b0c0d0e0f",
+    "ssrc_a": "0x12345678",
+    "ssrc_b": "0x98765432",
+    "stream_key_a": "f309f118aecdacfbc165cc080022b297100bbb55e483b002d762000a0faa684d",
+    "stream_key_b": "06e5d1b8c6e01f10b592bd2e13ff4b37182b895ec8330d5cc6ec690704043b5f"
+  },
+  {
+    "cipher_suite": 4,
+    "base_key": "000102030405060708090a0b0c0d0e0f",
+    "ssrc_a": "0x12345678",
+    "ssrc_b": "0x98765432",
+    "stream_key_a": "f309f118aecdacfbc165cc080022b297100bbb55e483b002d762000a0faa684d",
+    "stream_key_b": "06e5d1b8c6e01f10b592bd2e13ff4b37182b895ec8330d5cc6ec690704043b5f"
+  },
+  {
+    "cipher_suite": 5,
+    "base_key": "000102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f",
+    "ssrc_a": "0x12345678",
+    "ssrc_b": "0x98765432",
+    "stream_key_a": "4715e2a3e3ecb408c83135a30b8e660c75a3488dbd4d9dd3553a01b39df76bc43a5a0b130159edd90353b09c810e849db7398182ac7c1dea072a2c1b6bac7dda",
+    "stream_key_b": "f7891c6b18d88a93ba7638875b87146df4cb9693ca3837b480e9221539e86c1c98391cb1273423b33f94abe7f67c1070997a588084a54391ebda18b3d6ff92f1"
+  },
+  {
+    "cipher_suite": 6,
+    "base_key": "000102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f",
+    "ssrc_a": "0x12345678",
+    "ssrc_b": "0x98765432",
+    "stream_key_a": "4715e2a3e3ecb408c83135a30b8e660c75a3488dbd4d9dd3553a01b39df76bc43a5a0b130159edd90353b09c810e849db7398182ac7c1dea072a2c1b6bac7dda",
+    "stream_key_b": "f7891c6b18d88a93ba7638875b87146df4cb9693ca3837b480e9221539e86c1c98391cb1273423b33f94abe7f67c1070997a588084a54391ebda18b3d6ff92f1"
+  },
+  {
+    "cipher_suite": 7,
+    "base_key": "000102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f",
+    "ssrc_a": "0x12345678",
+    "ssrc_b": "0x98765432",
+    "stream_key_a": "4715e2a3e3ecb408c83135a30b8e660c75a3488dbd4d9dd3553a01b39df76bc43a5a0b130159edd90353b09c810e849db7398182ac7c1dea072a2c1b6bac7dda",
+    "stream_key_b": "f7891c6b18d88a93ba7638875b87146df4cb9693ca3837b480e9221539e86c1c98391cb1273423b33f94abe7f67c1070997a588084a54391ebda18b3d6ff92f1"
+  },
+  {
+    "cipher_suite": 8,
+    "base_key": "000102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f",
+    "ssrc_a": "0x12345678",
+    "ssrc_b": "0x98765432",
+    "stream_key_a": "4715e2a3e3ecb408c83135a30b8e660c75a3488dbd4d9dd3553a01b39df76bc43a5a0b130159edd90353b09c810e849db7398182ac7c1dea072a2c1b6bac7dda",
+    "stream_key_b": "f7891c6b18d88a93ba7638875b87146df4cb9693ca3837b480e9221539e86c1c98391cb1273423b33f94abe7f67c1070997a588084a54391ebda18b3d6ff92f1"
+  }
+]