Support key_derivation_rate and fix update_session_keys only working by accident
Jonas Herzig
parent
febcc71ac8
commit
0b5229d36f
109
src/rfc3711.rs
109
src/rfc3711.rs
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@ -40,6 +40,9 @@ pub struct SrtpContext {
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// TODO: support other fields
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pub master_key: Vec<u8>,
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pub master_salt: Vec<u8>,
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// Since actual kdr is a power of two, this only stores the power (+1).
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// i.e. actual kdr is 2^(key_derivation_rate-1) (or 0 in case of 0)
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pub key_derivation_rate: u8,
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pub rollover_counter: u32,
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pub highest_recv_seq_num: u16,
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pub encryption: EncryptionAlgorithm,
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@ -56,6 +59,7 @@ impl SrtpContext {
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SrtpContext {
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master_key: Vec::from(master_key),
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master_salt: Vec::from(master_salt),
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key_derivation_rate: 0,
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rollover_counter: 0,
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highest_recv_seq_num: 0,
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encryption: EncryptionAlgorithm::default(),
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@ -67,8 +71,16 @@ impl SrtpContext {
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auth_tag_len: 80 / 8,
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}
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}
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pub fn update_session_keys(&mut self) {
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let index = ((self.rollover_counter as u64) << 16) + self.highest_recv_seq_num as u64;
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pub fn update_session_keys(&mut self, index: u64) {
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let index = if self.key_derivation_rate == 0 {
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0
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} else {
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index >> (self.key_derivation_rate - 1)
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};
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// TODO: only recalculate if index changed, probably also cache surrounding indices
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// but make sure the initial updates happens
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let index = BigUint::from(index);
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let enc_key_id = BigUint::from_bytes_be(&[0, 0, 0, 0, 0, 0, 0]) + index.clone();
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@ -154,6 +166,45 @@ impl SrtpContext {
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};
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(probable_roc, ((probable_roc as PacketIndex) << 16) + seq_num as PacketIndex)
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}
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// https://tools.ietf.org/html/rfc3711#section-3.3
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pub fn process_incoming(&mut self, packet: &[u8]) -> Result<Vec<u8>> {
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// Step 1: determining the correct context (has already happened at this point)
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// Step 2: Determine index of the SRTP packet
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let reader = &mut &packet[..];
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let header = track_try!(rfc3550::RtpFixedHeader::read_from(reader));
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let seq_num = header.seq_num;
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let (rollover_counter, index) = self.estimate_packet_index(seq_num);
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// Step 3: Determine master key and salt
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// TODO: support re-keying
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// TODO: support MKI
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// Step 4: Determine session keys and salt
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self.update_session_keys(index);
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// Step 5: Replay protection and authentication
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// TODO: replay protection
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self.authenticate(packet)?;
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// Step 6: Decryption
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let result = self.decrypt(packet)?;
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// Step 7: Update ROC, highest sequence number and replay protection
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// TODO: replay protection
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// https://tools.ietf.org/html/rfc3711#section-3.3.1
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if rollover_counter == self.rollover_counter {
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if seq_num > self.highest_recv_seq_num {
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self.highest_recv_seq_num = seq_num;
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}
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} else if rollover_counter > self.rollover_counter {
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self.highest_recv_seq_num = seq_num;
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self.rollover_counter = rollover_counter;
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}
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Ok(result)
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}
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}
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#[derive(Debug, Clone, PartialEq, Eq)]
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@ -161,6 +212,9 @@ pub struct SrtcpContext {
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// TODO: support other fields
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pub master_key: Vec<u8>,
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pub master_salt: Vec<u8>,
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// Since actual kdr is a power of two, this only stores the power (+1).
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// i.e. actual kdr is 2^(key_derivation_rate-1) (or 0 in case of 0)
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pub key_derivation_rate: u8,
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pub highest_recv_index: u32, // NOTE: 31-bits
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pub encryption: EncryptionAlgorithm,
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pub authentication: AuthenticationAlgorithm,
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@ -176,6 +230,7 @@ impl SrtcpContext {
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SrtcpContext {
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master_key: Vec::from(master_key),
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master_salt: Vec::from(master_salt),
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key_derivation_rate: 0,
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highest_recv_index: 0,
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encryption: EncryptionAlgorithm::default(),
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authentication: AuthenticationAlgorithm::default(),
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@ -186,9 +241,18 @@ impl SrtcpContext {
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auth_tag_len: 80 / 8,
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}
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}
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pub fn update_session_keys(&mut self) {
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pub fn update_session_keys(&mut self, index: u32) {
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let index = if self.key_derivation_rate == 0 {
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0
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} else {
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index >> (self.key_derivation_rate - 1)
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};
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// TODO: only recalculate if index changed, probably also cache surrounding indices
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// but make sure the initial updates happens
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// See: https://tools.ietf.org/html/rfc3711#section-4.3.2
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let index = BigUint::from(self.highest_recv_index);
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let index = BigUint::from(index);
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let enc_key_id = BigUint::from_bytes_be(&[3, 0, 0, 0, 0, 0, 0]) + index.clone();
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let auth_key_id = BigUint::from_bytes_be(&[4, 0, 0, 0, 0, 0, 0]) + index.clone();
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@ -251,6 +315,35 @@ impl SrtcpContext {
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Ok(decrypted)
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}
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// https://tools.ietf.org/html/rfc3711#section-3.3
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// https://tools.ietf.org/html/rfc3711#section-3.4
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pub fn process_incoming(&mut self, packet: &[u8]) -> Result<Vec<u8>> {
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// Step 1: determining the correct context (has already happened at this point)
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// Step 2: Determine index of the SRTCP packet
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let index = track_try!((&mut &packet[packet.len() - self.auth_tag_len - 4..]).read_u32be());
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let index = index & 0x7FFF_FFFF; // remove uppermost bit which isn't part of the index
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// Step 3: Determine master key and salt
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// TODO: support re-keying
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// TODO: support MKI
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// Step 4: Determine session keys and salt
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self.update_session_keys(index);
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// Step 5: Replay protection and authentication
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// TODO: replay protection
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track_try!(self.authenticate(packet));
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// Step 6: Decryption
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let result = track_try!(self.decrypt(packet));
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// Step 7: Update replay protection
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// TODO: replay protection
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Ok(result)
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}
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}
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#[derive(Debug, Clone, PartialEq, Eq)]
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@ -264,7 +357,6 @@ where
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T::Packet: RtpPacket,
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{
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pub fn new(mut context: SrtpContext, inner: T) -> Self {
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context.update_session_keys();
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SrtpPacketReader {
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context: context,
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inner: inner,
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@ -279,8 +371,7 @@ where
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type Packet = T::Packet;
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fn read_packet<R: Read>(&mut self, reader: &mut R) -> Result<Self::Packet> {
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let packet_bytes = track_try!(reader.read_all_bytes());
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track_try!(self.context.authenticate(&packet_bytes));
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let decrypted_packet_bytes = track_try!(self.context.decrypt(&packet_bytes));
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let decrypted_packet_bytes = track_try!(self.context.process_incoming(&packet_bytes));
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track_err!(self.inner.read_packet(&mut &decrypted_packet_bytes[..]))
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}
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@ -300,7 +391,6 @@ where
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T::Packet: RtcpPacket,
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{
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pub fn new(mut context: SrtcpContext, inner: T) -> Self {
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context.update_session_keys();
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SrtcpPacketReader {
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context: context,
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inner: inner,
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@ -315,8 +405,7 @@ where
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type Packet = T::Packet;
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fn read_packet<R: Read>(&mut self, reader: &mut R) -> Result<Self::Packet> {
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let packet_bytes = track_try!(reader.read_all_bytes());
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track_try!(self.context.authenticate(&packet_bytes));
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let decrypted_packet_bytes = track_try!(self.context.decrypt(&packet_bytes));
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let decrypted_packet_bytes = track_try!(self.context.process_incoming(&packet_bytes));
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track_err!(self.inner.read_packet(&mut &decrypted_packet_bytes[..]))
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}
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