fatedier/frp · error

no supported crypto algorithm

Error message

no supported crypto algorithm

What it means

During ServerHello construction the server found no AEAD algorithm in common with the client: SelectAEADAlgorithm walked clientHello.Capabilities.Crypto.Algorithms and none matched the server's supported set (aes-256-gcm, xchacha20-poly1305). The wire v2 protocol requires at least one shared AEAD before encryption can be negotiated.

Solutions

1. Run the same (or compatible) frp version on both ends so both advertise aes-256-gcm / xchacha20-poly1305
2. If on unusual hardware, verify the build supports at least one of the two AEADs (both are pure-Go capable)
3. For custom clients, include at least one of the supported algorithm strings in the ClientHello capabilities

Example fix

// before (custom client)
hello.Capabilities.Crypto.Algorithms = []string{"my-aead"}

// after
hello.Capabilities.Crypto.Algorithms = []string{
  wire.AEADAlgorithmAES256GCM,
  wire.AEADAlgorithmXChaCha20Poly1305,
}

// Offer both supported algorithms before connecting
hello.Capabilities.Crypto.Algorithms = []string{
    wire.AEADAlgorithmAES256GCM,
    wire.AEADAlgorithmXChaCha20Poly1305,
}

if _, err := wire.NewServerHello(clientHello); err != nil && strings.Contains(err.Error(), "no supported crypto algorithm") {
    // peer advertises incompatible algorithms: refuse instead of retrying
    return errors.New("incompatible peer crypto capabilities")
}

When it happens

Trigger: NewServerHello with a ClientHello whose crypto algorithm list is empty or contains only algorithms this build does not support (or HW acceleration unavailable so AES-GCM/XChaCha20 is disabled).

Common situations: Cross-version connection where an older/other-party client advertises different algorithm names; a custom/forked client with a trimmed algorithm list; capability list lost/mangled in transit.

Related errors

• invalid crypto client random length
• decode ClientHello transcript
• decode ServerHello transcript
• invalid crypto server random length
• missing v2 crypto negotiation

AI-assisted analysis of fatedier/frp@6c8a8d0a97 (2026-08-15). Data as JSON: /api/errors/6596ba0f40b6e035. Report an issue: GitHub.

Appendix: source

Thrown at pkg/proto/wire/crypto.go:62

	Algorithm      string
	TranscriptHash []byte
}

func NewClientHello(bootstrap BootstrapInfo) (ClientHello, error) {
	clientRandom, err := newCryptoRandom()
	if err != nil {
		return ClientHello{}, err
	}
	return clientHelloWithCryptoRandom(bootstrap, clientRandom), nil
}

func NewServerHello(clientHello ClientHello) (ServerHello, error) {
	if err := ValidateClientHello(clientHello); err != nil {
		return ServerHello{}, err
	}
	algorithm, ok := SelectAEADAlgorithm(clientHello.Capabilities.Crypto.Algorithms)
	if !ok {
		return ServerHello{}, fmt.Errorf("no supported crypto algorithm")
	}
	serverRandom, err := newCryptoRandom()
	if err != nil {
		return ServerHello{}, err
	}
	return ServerHello{
		Selected: ServerSelection{
			Message: MessageSelection{
				Codec:          MessageCodecJSON,
				UDPPacketCodec: selectUDPPacketCodec(clientHello.Capabilities.Message.UDPPacketCodecs),
			},
			Crypto: CryptoSelection{
				Algorithm:    algorithm,
				ServerRandom: serverRandom,
			},
		},
	}, nil
}

View on GitHub (pinned to 6c8a8d0a97)