151 lines
3.2 KiB
Go
151 lines
3.2 KiB
Go
package varsig
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import (
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"crypto/ed25519"
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"encoding/binary"
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"fmt"
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)
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// DiscriminatorEdDSA is the value specifying an EdDSA signature.
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const DiscriminatorEdDSA = Discriminator(0xed)
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// EdDSACurve are values that specify which Edwards curve is used when
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// generating the signature.
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type EdDSACurve uint64
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// Constants describing the values for each specific Edwards curve that can
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// be encoded into a Varsig.
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const (
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CurveEd25519 = EdDSACurve(0xed)
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CurveEd448 = EdDSACurve(0x1203)
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)
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func decodeEdDSACurve(r BytesReader) (EdDSACurve, error) {
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u, err := binary.ReadUvarint(r)
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if err != nil {
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return 0, err
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}
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switch curve := EdDSACurve(u); curve {
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case CurveEd25519, CurveEd448:
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return curve, nil
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default:
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return 0, fmt.Errorf("%w: %x", ErrUnknownEdDSACurve, u)
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}
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}
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var _ Varsig = EdDSAVarsig{}
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// EdDSAVarsig is a varsig that encodes the parameters required to describe
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// an EdDSA signature.
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type EdDSAVarsig struct {
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varsig
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curve EdDSACurve
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hashAlg Hash
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}
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// NewEdDSAVarsig creates and validates an EdDSA varsig with the provided
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// curve, hash algorithm and payload encoding.
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func NewEdDSAVarsig(curve EdDSACurve, hashAlgorithm Hash, payloadEncoding PayloadEncoding, opts ...Option) (EdDSAVarsig, error) {
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options := newOptions(opts...)
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var (
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vers = Version1
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disc = DiscriminatorEdDSA
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sig []byte
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)
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if options.ForceVersion0() {
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vers = Version0
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disc = Discriminator(curve)
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sig = options.Signature()
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}
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v := EdDSAVarsig{
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varsig: varsig{
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vers: vers,
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disc: disc,
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payEnc: payloadEncoding,
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sig: sig,
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},
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curve: curve,
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hashAlg: hashAlgorithm,
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}
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switch curve {
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case CurveEd25519:
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return validateSig(v, ed25519.SignatureSize)
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case CurveEd448:
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return validateSig(v, 114)
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default:
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return EdDSAVarsig{}, fmt.Errorf("%w: %x", ErrUnknownEdDSACurve, curve)
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}
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}
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// Curve returns the Edwards curve used to generate the EdDSA signature.
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func (v EdDSAVarsig) Curve() EdDSACurve {
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return v.curve
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}
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// Hash returns the value describing the hash algorithm used to hash
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// the payload content before the signature is generated.
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func (v EdDSAVarsig) Hash() Hash {
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return v.hashAlg
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}
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// Encode returns the encoded byte format of the EdDSAVarsig.
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func (v EdDSAVarsig) Encode() []byte {
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buf := v.encode()
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if v.vers != Version0 {
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buf = binary.AppendUvarint(buf, uint64(v.curve))
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}
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buf = binary.AppendUvarint(buf, uint64(v.hashAlg))
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buf = binary.AppendUvarint(buf, uint64(v.payEnc))
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buf = append(buf, v.Signature()...)
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return buf
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}
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func decodeEdDSA(r BytesReader, vers Version, disc Discriminator) (Varsig, error) {
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curve := EdDSACurve(disc)
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if vers != Version0 {
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var err error
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curve, err = decodeEdDSACurve(r)
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if err != nil {
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return nil, err
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}
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}
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hashAlg, err := DecodeHashAlgorithm(r)
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if err != nil {
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return nil, err
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}
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v := EdDSAVarsig{
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varsig: varsig{
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vers: vers,
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disc: disc,
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},
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curve: curve,
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hashAlg: hashAlg,
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}
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v.payEnc, v.sig, err = v.decodePayEncAndSig(r)
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if err != nil {
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return nil, err
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}
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switch curve {
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case CurveEd25519:
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return validateSig(v, ed25519.SignatureSize)
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case CurveEd448:
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return validateSig(v, 114)
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default:
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return EdDSAVarsig{}, fmt.Errorf("%w: %x", ErrUnknownEdDSACurve, curve)
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}
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}
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