131 lines
3.5 KiB
Go
131 lines
3.5 KiB
Go
// Package varsig implements v1.0.0 of the [Varsig specification] with
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// limited support for varsig < v1. This is primarily in support of the
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// UCAN v1.0.0 specification and will be deprecated in the future.
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//
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// # Common algorithm naming
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//
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// While there is no strict need for compatibility with JWA/JWT/JWE/JWS,
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// all attempts are made to keep the algorithm names here consistent with
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// list made available at the [IANA Registry] titled "JSON Web Signature
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// and Encryption Algorithms" (JOSE.)
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//
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// It should also be noted that algorithm in this context might in fact be
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// a pseudonym - for cryptographical signing algorithms that require the
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// signed data to be hashed first, these names commonly refer to the
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// combination of that signing algorithm and the hash algorithm.
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//
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// [IANA Registry]]: https://www.iana.org/assignments/jose/jose.xhtml#web-signature-encryption-algorithms
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// [Varsig Specification]: https://github.com/ChainAgnostic/varsig
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package varsig
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import (
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"bytes"
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"encoding/binary"
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"io"
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)
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// Varsig represents types that describe how a signature was generated
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// and thus how to interpret the signature and verify the signed data.
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type Varsig interface {
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// accessors for fields that are common to all varsig
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Version() Version
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Discriminator() Discriminator
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PayloadEncoding() PayloadEncoding
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Signature() []byte
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// Operations that are common to all varsig
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Encode() []byte
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}
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// Decode converts the provided data into one of the Varsig types
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// provided by the DefaultRegistry.
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func Decode(data []byte) (Varsig, error) {
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return DefaultRegistry().Decode(data)
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}
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// DecodeStream converts data read from the provided io.Reader into one
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// of the Varsig types provided by the DefaultRegistry.
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func DecodeStream(r *bytes.Reader) (Varsig, error) {
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return DefaultRegistry().DecodeStream(r)
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}
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type varsig[T Varsig] struct {
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vers Version
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disc Discriminator
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payEnc PayloadEncoding
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sig []byte
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}
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// Version returns the varsig's version field.
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func (v varsig[_]) Version() Version {
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return v.vers
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}
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// Discriminator returns the algorithm used to produce corresponding
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// signature.
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func (v varsig[_]) Discriminator() Discriminator {
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return v.disc
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}
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// PayloadEncoding returns the codec that was used to encode the signed
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// data.
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func (v varsig[_]) PayloadEncoding() PayloadEncoding {
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return v.payEnc
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}
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// Signature returns the cryptographic signature of the signed data. This
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// value is never present in a varsig >= v1 and must either be a valid
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// signature with the correct length or empty in varsig < v1.
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func (v varsig[_]) Signature() []byte {
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return v.sig
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}
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func (v *varsig[_]) encode() []byte {
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var buf []byte
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buf = binary.AppendUvarint(buf, Prefix)
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if v.Version() == Version1 {
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buf = binary.AppendUvarint(buf, uint64(Version1))
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}
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buf = binary.AppendUvarint(buf, uint64(v.disc))
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return buf
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}
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func (v *varsig[T]) decodePayEncAndSig(r *bytes.Reader, varsig *T, expectedLength uint64) (*T, error) {
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payEnc, err := DecodePayloadEncoding(r, v.Version())
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if err != nil {
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return nil, err
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}
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v.payEnc = payEnc
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signature, err := io.ReadAll(r)
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if err != nil {
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return nil, err
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}
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v.sig = signature
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return v.validateSig(varsig, expectedLength)
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}
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func (v *varsig[T]) validateSig(varsig *T, expectedLength uint64) (*T, error) {
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if v.Version() == Version0 && len(v.sig) == 0 {
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return varsig, ErrMissingSignature
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}
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if v.Version() == Version0 && uint64(len(v.sig)) != expectedLength {
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return nil, ErrUnexpectedSignatureSize
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}
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if v.Version() == Version1 && len(v.sig) != 0 {
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return nil, ErrUnexpectedSignaturePresent
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}
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return varsig, nil
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}
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