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|
package srtp
import (
"fmt"
"github.com/pion/transport/replaydetector"
)
const (
labelSRTPEncryption = 0x00
labelSRTPAuthenticationTag = 0x01
labelSRTPSalt = 0x02
labelSRTCPEncryption = 0x03
labelSRTCPAuthenticationTag = 0x04
labelSRTCPSalt = 0x05
maxROCDisorder = 100
maxSequenceNumber = 65535
srtcpIndexSize = 4
)
// Encrypt/Decrypt state for a single SRTP SSRC
type srtpSSRCState struct {
ssrc uint32
rolloverCounter uint32
rolloverHasProcessed bool
lastSequenceNumber uint16
replayDetector replaydetector.ReplayDetector
}
// Encrypt/Decrypt state for a single SRTCP SSRC
type srtcpSSRCState struct {
srtcpIndex uint32
ssrc uint32
replayDetector replaydetector.ReplayDetector
}
// Context represents a SRTP cryptographic context.
// Context can only be used for one-way operations.
// it must either used ONLY for encryption or ONLY for decryption.
type Context struct {
cipher srtpCipher
srtpSSRCStates map[uint32]*srtpSSRCState
srtcpSSRCStates map[uint32]*srtcpSSRCState
newSRTCPReplayDetector func() replaydetector.ReplayDetector
newSRTPReplayDetector func() replaydetector.ReplayDetector
}
// CreateContext creates a new SRTP Context.
//
// CreateContext receives variable number of ContextOption-s.
// Passing multiple options which set the same parameter let the last one valid.
// Following example create SRTP Context with replay protection with window size of 256.
//
// decCtx, err := srtp.CreateContext(key, salt, profile, srtp.SRTPReplayProtection(256))
//
func CreateContext(masterKey, masterSalt []byte, profile ProtectionProfile, opts ...ContextOption) (c *Context, err error) {
keyLen, err := profile.keyLen()
if err != nil {
return nil, err
}
saltLen, err := profile.saltLen()
if err != nil {
return nil, err
}
if masterKeyLen := len(masterKey); masterKeyLen != keyLen {
return c, fmt.Errorf("%w expected(%d) actual(%d)", errShortSrtpMasterKey, masterKey, keyLen)
} else if masterSaltLen := len(masterSalt); masterSaltLen != saltLen {
return c, fmt.Errorf("%w expected(%d) actual(%d)", errShortSrtpMasterSalt, saltLen, masterSaltLen)
}
c = &Context{
srtpSSRCStates: map[uint32]*srtpSSRCState{},
srtcpSSRCStates: map[uint32]*srtcpSSRCState{},
}
switch profile {
case ProtectionProfileAeadAes128Gcm:
c.cipher, err = newSrtpCipherAeadAesGcm(masterKey, masterSalt)
case ProtectionProfileAes128CmHmacSha1_80:
c.cipher, err = newSrtpCipherAesCmHmacSha1(masterKey, masterSalt)
default:
return nil, fmt.Errorf("%w: %#v", errNoSuchSRTPProfile, profile)
}
if err != nil {
return nil, err
}
for _, o := range append(
[]ContextOption{ // Default options
SRTPNoReplayProtection(),
SRTCPNoReplayProtection(),
},
opts..., // User specified options
) {
if errOpt := o(c); errOpt != nil {
return nil, errOpt
}
}
return c, nil
}
// https://tools.ietf.org/html/rfc3550#appendix-A.1
func (s *srtpSSRCState) nextRolloverCount(sequenceNumber uint16) (uint32, func()) {
roc := s.rolloverCounter
switch {
case !s.rolloverHasProcessed:
case sequenceNumber == 0: // We exactly hit the rollover count
// Only update rolloverCounter if lastSequenceNumber is greater then maxROCDisorder
// otherwise we already incremented for disorder
if s.lastSequenceNumber > maxROCDisorder {
roc++
}
case s.lastSequenceNumber < maxROCDisorder &&
sequenceNumber > (maxSequenceNumber-maxROCDisorder):
// Our last sequence number incremented because we crossed 0, but then our current number was within maxROCDisorder of the max
// So we fell behind, drop to account for jitter
roc--
case sequenceNumber < maxROCDisorder &&
s.lastSequenceNumber > (maxSequenceNumber-maxROCDisorder):
// our current is within a maxROCDisorder of 0
// and our last sequence number was a high sequence number, increment to account for jitter
roc++
}
return roc, func() {
s.rolloverHasProcessed = true
s.lastSequenceNumber = sequenceNumber
s.rolloverCounter = roc
}
}
func (c *Context) getSRTPSSRCState(ssrc uint32) *srtpSSRCState {
s, ok := c.srtpSSRCStates[ssrc]
if ok {
return s
}
s = &srtpSSRCState{
ssrc: ssrc,
replayDetector: c.newSRTPReplayDetector(),
}
c.srtpSSRCStates[ssrc] = s
return s
}
func (c *Context) getSRTCPSSRCState(ssrc uint32) *srtcpSSRCState {
s, ok := c.srtcpSSRCStates[ssrc]
if ok {
return s
}
s = &srtcpSSRCState{
ssrc: ssrc,
replayDetector: c.newSRTCPReplayDetector(),
}
c.srtcpSSRCStates[ssrc] = s
return s
}
// ROC returns SRTP rollover counter value of specified SSRC.
func (c *Context) ROC(ssrc uint32) (uint32, bool) {
s, ok := c.srtpSSRCStates[ssrc]
if !ok {
return 0, false
}
return s.rolloverCounter, true
}
// SetROC sets SRTP rollover counter value of specified SSRC.
func (c *Context) SetROC(ssrc uint32, roc uint32) {
s := c.getSRTPSSRCState(ssrc)
s.rolloverCounter = roc
}
// Index returns SRTCP index value of specified SSRC.
func (c *Context) Index(ssrc uint32) (uint32, bool) {
s, ok := c.srtcpSSRCStates[ssrc]
if !ok {
return 0, false
}
return s.srtcpIndex, true
}
// SetIndex sets SRTCP index value of specified SSRC.
func (c *Context) SetIndex(ssrc uint32, index uint32) {
s := c.getSRTCPSSRCState(ssrc)
s.srtcpIndex = index % (maxSRTCPIndex + 1)
}
|
