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package srtp
const labelExtractorDtlsSrtp = "EXTRACTOR-dtls_srtp"
// KeyingMaterialExporter allows package SRTP to extract keying material
type KeyingMaterialExporter interface {
ExportKeyingMaterial(label string, context []byte, length int) ([]byte, error)
}
// ExtractSessionKeysFromDTLS allows setting the Config SessionKeys by
// extracting them from DTLS. This behavior is defined in RFC5764:
// https://tools.ietf.org/html/rfc5764
func (c *Config) ExtractSessionKeysFromDTLS(exporter KeyingMaterialExporter, isClient bool) error {
keyLen, err := c.Profile.keyLen()
if err != nil {
return err
}
saltLen, err := c.Profile.saltLen()
if err != nil {
return err
}
keyingMaterial, err := exporter.ExportKeyingMaterial(labelExtractorDtlsSrtp, nil, (keyLen*2)+(saltLen*2))
if err != nil {
return err
}
offset := 0
clientWriteKey := append([]byte{}, keyingMaterial[offset:offset+keyLen]...)
offset += keyLen
serverWriteKey := append([]byte{}, keyingMaterial[offset:offset+keyLen]...)
offset += keyLen
clientWriteKey = append(clientWriteKey, keyingMaterial[offset:offset+saltLen]...)
offset += saltLen
serverWriteKey = append(serverWriteKey, keyingMaterial[offset:offset+saltLen]...)
if isClient {
c.Keys.LocalMasterKey = clientWriteKey[0:keyLen]
c.Keys.LocalMasterSalt = clientWriteKey[keyLen:]
c.Keys.RemoteMasterKey = serverWriteKey[0:keyLen]
c.Keys.RemoteMasterSalt = serverWriteKey[keyLen:]
return nil
}
c.Keys.LocalMasterKey = serverWriteKey[0:keyLen]
c.Keys.LocalMasterSalt = serverWriteKey[keyLen:]
c.Keys.RemoteMasterKey = clientWriteKey[0:keyLen]
c.Keys.RemoteMasterSalt = clientWriteKey[keyLen:]
return nil
}
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