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

pkg/mikey/sub_payload_key_data.go

@@ -0,0 +1,66 @@
+package mikey
+
+import "fmt"
+
+// SubPayloadKeyDataKeyType is a data key type.
+type SubPayloadKeyDataKeyType uint8
+
+// RFC3830, table 6.13.a
+const (
+	SubPayloadKeyDataKeyTypeTEK SubPayloadKeyDataKeyType = 2
+)
+
+// SubPayloadKeyData is a key data sub-payload.
+type SubPayloadKeyData struct {
+	Type    SubPayloadKeyDataKeyType
+	KV      uint8
+	KeyData []byte
+}
+
+func (p *SubPayloadKeyData) unmarshal(buf []byte) (int, error) {
+	if len(buf) < 4 {
+		return 0, fmt.Errorf("buffer too short")
+	}
+
+	n := 1
+	p.Type = SubPayloadKeyDataKeyType(buf[n] >> 4)
+	p.KV = buf[n] & 0b00001111
+	n++
+
+	if p.Type != SubPayloadKeyDataKeyTypeTEK {
+		return 0, fmt.Errorf("unsupported key type: %v", p.Type)
+	}
+
+	if p.KV != 0 {
+		return 0, fmt.Errorf("unsupported KV: %v", p.KV)
+	}
+
+	keyDataLen := int(uint16(buf[n])<<8 | uint16(buf[n+1]))
+	n += 2
+
+	if len(buf[n:]) < keyDataLen {
+		return 0, fmt.Errorf("buffer too short")
+	}
+
+	p.KeyData = buf[n : n+keyDataLen]
+	n += keyDataLen
+
+	return n, nil
+}
+
+func (p *SubPayloadKeyData) marshalSize() int {
+	return 4 + len(p.KeyData)
+}
+
+func (p *SubPayloadKeyData) marshalTo(buf []byte) (int, error) {
+	buf[1] = byte(p.Type)<<4 | p.KV
+
+	keyDataLen := len(p.KeyData)
+	buf[2] = byte(keyDataLen >> 8)
+	buf[3] = byte(keyDataLen)
+	n := 4
+
+	n += copy(buf[n:], p.KeyData)
+
+	return n, nil
+}