nuts-foundation/nuts-node

/*
 * Copyright (C) 2023 Nuts community
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 *
 */

package didkey

import (
    "bytes"
    "crypto"
    "crypto/ecdsa"
    "crypto/ed25519"
    "crypto/elliptic"
    "crypto/x509"
    "encoding/binary"
    "errors"
    "fmt"
    "github.com/lestrrat-go/jwx/v2/x25519"
    "github.com/mr-tron/base58"
    "github.com/multiformats/go-multicodec"
    ssi "github.com/nuts-foundation/go-did"
    "github.com/nuts-foundation/go-did/did"
    "github.com/nuts-foundation/nuts-node/vdr/resolver"
    "io"
)

// MethodName is the name of this DID method.
const MethodName = "key"

var _ resolver.DIDResolver = &Resolver{}

var errInvalidPublicKeyLength = errors.New("invalid did:key: invalid public key length")

// NewResolver creates a new Resolver.
func NewResolver() *Resolver {
    return &Resolver{}
}

type Resolver struct {
}

func (r Resolver) Resolve(id did.DID, _ *resolver.ResolveMetadata) (*did.Document, *resolver.DocumentMetadata, error) {
    if id.Method != MethodName {
        return nil, nil, fmt.Errorf("unsupported DID method: %s", id.Method)
    }
    encodedKey := id.ID
    if len(encodedKey) == 0 || encodedKey[0] != 'z' {
        return nil, nil, errors.New("did:key does not start with 'z'")
    }
    mcBytes, err := base58.DecodeAlphabet(encodedKey[1:], base58.BTCAlphabet)
    if err != nil {
        return nil, nil, fmt.Errorf("did:key: invalid base58btc: %w", err)
    }
    reader := bytes.NewReader(mcBytes)
    keyType, err := binary.ReadUvarint(reader)
    if err != nil {
        return nil, nil, fmt.Errorf("did:key: invalid multicodec value: %w", err)
    }
    // See https://w3c-ccg.github.io/did-method-key/#signature-method-creation-algorithm
    var key crypto.PublicKey
    mcBytes, _ = io.ReadAll(reader)
    keyLength := len(mcBytes)

    switch multicodec.Code(keyType) {
    case multicodec.Bls12_381G2Pub:
        return nil, nil, errors.New("did:key: bls12381 public keys are not supported")
    case multicodec.X25519Pub:
        if keyLength != 32 {
            return nil, nil, errInvalidPublicKeyLength
        }
        key = x25519.PublicKey(mcBytes)
    case multicodec.Ed25519Pub:
        if keyLength != 32 {
            return nil, nil, errInvalidPublicKeyLength
        }
        key = ed25519.PublicKey(mcBytes)
    case multicodec.Secp256k1Pub:
        // lestrrat/jwk.FromRaw() is missing support for secp256k1
        return nil, nil, errors.New("did:key: secp256k1 public keys are not supported")
    case multicodec.P256Pub:
        if key, err = unmarshalEC(elliptic.P256(), 33, mcBytes); err != nil {
            return nil, nil, err
        }
    case multicodec.P384Pub:
        if key, err = unmarshalEC(elliptic.P384(), 49, mcBytes); err != nil {
            return nil, nil, err
        }
    case multicodec.P521Pub:
        key, _ = unmarshalEC(elliptic.P521(), -1, mcBytes)
    case multicodec.RsaPub:
        rsaKey, err := x509.ParsePKCS1PublicKey(mcBytes)
        if err != nil {
            return nil, nil, fmt.Errorf("did:key: invalid PKCS#1 encoded RSA public key: %w", err)
        }
        // Safe RSA keys must be at least 2048 bits
        if rsaKey.Size() < 256 {
            return nil, nil, errors.New("did:key: RSA public key is too small (must be at least 2048 bits)")
        }
        key = rsaKey
    default:
        return nil, nil, fmt.Errorf("did:key: unsupported public key type: 0x%x", keyType)
    }

    document := did.Document{
        Context: []interface{}{
            ssi.MustParseURI("https://w3c-ccg.github.io/lds-jws2020/contexts/lds-jws2020-v1.json"),
            did.DIDContextV1URI(),
        },
        ID: id,
    }
    keyID := did.DIDURL{DID: id}
    keyID.Fragment = id.ID
    vm, err := did.NewVerificationMethod(keyID, ssi.JsonWebKey2020, id, key)
    if err != nil {
        return nil, nil, err
    }
    document.AddAssertionMethod(vm)
    document.AddAuthenticationMethod(vm)
    document.AddKeyAgreement(vm)
    document.AddCapabilityDelegation(vm)
    document.AddCapabilityInvocation(vm)
    return &document, &resolver.DocumentMetadata{}, nil
}

func unmarshalEC(curve elliptic.Curve, expectedLen int, pubKeyBytes []byte) (ecdsa.PublicKey, error) {
    if expectedLen != -1 && len(pubKeyBytes) != expectedLen {
        return ecdsa.PublicKey{}, errInvalidPublicKeyLength
    }
    x, y := elliptic.UnmarshalCompressed(curve, pubKeyBytes)
    return ecdsa.PublicKey{Curve: curve, X: x, Y: y}, nil
}