support encrypted streams with SRTP and MIKEY (#520) (#809)

pkg/mikey/payload_sp.go

@@ -0,0 +1,129 @@
+package mikey
+
+import "fmt"
+
+// PayloadSPProtType is a security protocol.
+type PayloadSPProtType uint8
+
+// RFC3830, Table 6.2.a
+const (
+	PayloadSPProtTypeSRTP PayloadSPProtType = 0
+)
+
+// PayloadSPPolicyParamType is a policy param type.
+type PayloadSPPolicyParamType uint8
+
+// RFC3830, Table 6.10.1.a
+const (
+	PayloadSPPolicyParamTypeEncrAlg           PayloadSPPolicyParamType = 0
+	PayloadSPPolicyParamTypeSessionEncrKeyLen PayloadSPPolicyParamType = 1
+	PayloadSPPolicyParamTypeAuthAlg           PayloadSPPolicyParamType = 2
+	PayloadSPPolicyParamTypeSessionAuthKeyLen PayloadSPPolicyParamType = 3
+	PayloadSPPolicyParamTypeSessionSaltKeyLen PayloadSPPolicyParamType = 4
+	PayloadSPPolicyParamTypeSRTPPseudoRandFun PayloadSPPolicyParamType = 5
+	PayloadSPPolicyParamTypeKeyDerRate        PayloadSPPolicyParamType = 6
+	PayloadSPPolicyParamTypeSRTPEncrOffOn     PayloadSPPolicyParamType = 7
+	PayloadSPPolicyParamTypeSRTCPEncrOffOn    PayloadSPPolicyParamType = 8
+	PayloadSPPolicyParamTypeSenderFECOrder    PayloadSPPolicyParamType = 9
+	PayloadSPPolicyParamTypeSRTPAuthOffOn     PayloadSPPolicyParamType = 10
+	PayloadSPPolicyParamTypeAuthTagLen        PayloadSPPolicyParamType = 11
+	PayloadSPPolicyParamTypeSRTPPrefixLen     PayloadSPPolicyParamType = 12
+)
+
+// PayloadSPPolicyParam is a policy param.
+type PayloadSPPolicyParam struct {
+	Type  PayloadSPPolicyParamType
+	Value []byte
+}
+
+// PayloadSP is a security policy payload.
+type PayloadSP struct {
+	PolicyNo     uint8
+	ProtType     PayloadSPProtType
+	PolicyParams []PayloadSPPolicyParam
+}
+
+func (p *PayloadSP) unmarshal(buf []byte) (int, error) {
+	if len(buf) < 5 {
+		return 0, fmt.Errorf("buffer too short")
+	}
+
+	n := 1
+	p.PolicyNo = buf[n]
+	n++
+	p.ProtType = PayloadSPProtType(buf[n])
+	n++
+
+	if p.ProtType != 0 {
+		return 0, fmt.Errorf("unsupported prot type: %v", p.ProtType)
+	}
+
+	policyParamLength := uint16(buf[n])<<8 | uint16(buf[n+1])
+	n += 2
+	end := n + int(policyParamLength)
+
+	for {
+		if n > end {
+			return 0, fmt.Errorf("policy param overflowed")
+		}
+		if n == end {
+			break
+		}
+		if len(buf[n:]) < 2 {
+			return 0, fmt.Errorf("buffer too short")
+		}
+
+		typ := PayloadSPPolicyParamType(buf[n])
+		n++
+		valueLen := int(buf[n])
+		n++
+
+		if len(buf[n:]) < valueLen {
+			return 0, fmt.Errorf("buffer too short")
+		}
+
+		value := buf[n : n+valueLen]
+		n += valueLen
+
+		p.PolicyParams = append(p.PolicyParams, PayloadSPPolicyParam{
+			Type:  typ,
+			Value: value,
+		})
+	}
+
+	return n, nil
+}
+
+func (*PayloadSP) typ() payloadType {
+	return payloadTypeSP
+}
+
+func (p *PayloadSP) marshalSize() int {
+	n := 5 + 2*len(p.PolicyParams)
+	for _, pp := range p.PolicyParams {
+		n += len(pp.Value)
+	}
+	return n
+}
+
+func (p *PayloadSP) marshalTo(buf []byte) (int, error) {
+	buf[1] = p.PolicyNo
+	buf[2] = byte(p.ProtType)
+
+	policyParamLength := 0
+	for _, pp := range p.PolicyParams {
+		policyParamLength += 2 + len(pp.Value)
+	}
+	buf[3] = byte(policyParamLength >> 8)
+	buf[4] = byte(policyParamLength)
+	n := 5
+
+	for _, pp := range p.PolicyParams {
+		buf[n] = byte(pp.Type)
+		buf[n+1] = uint8(len(pp.Value))
+		n += 2
+		n += copy(buf[n:], pp.Value)
+	}
+
+	return n, nil
+}