rename tokens to token

token/internal/varsig/varsig.go

@@ -0,0 +1,133 @@
+// Package varsig implements the portion of the [varsig specification]
+// that's needed for the UCAN [Envelope].
+//
+// While the [Envelope] specification has a field that's labelled
+// "VarsigHeader", this field is actually the prefix, header and segments
+// of the body excluding the signature itself (which is a different field
+// in the [Envelope]).
+//
+// Given that [go-ucan] supports a limited number of public key types,
+// and that the signature isn't part of the resulting field, the values
+// that are used are constants.  Note that for key types that are fully
+// specified in the [did:key], the [VarsigHeader] field isn't technically
+// needed and could theoretically conflict with the DID.
+//
+// Treating these values as constants has no impact when issuing or
+// delegating tokens.  When decoding tokens, simply matching the strings
+// will allow us to detect errors but won't provide as much detail (e.g.
+// we can't indicate that the signature was incorrectly generated from
+// a DAG-JSON encoding.)
+//
+// [varsig specification]: https://github.com/ChainAgnostic/varsig
+// [Envelope]:https://github.com/ucan-wg/spec#envelope
+// [go-ucan]: https://github.com/ucan-wg/go-ucan
+package varsig
+
+import (
+	"encoding/binary"
+	"errors"
+	"fmt"
+
+	"github.com/libp2p/go-libp2p/core/crypto/pb"
+	"github.com/multiformats/go-multicodec"
+)
+
+const (
+	Prefix = 0x34
+)
+
+// ErrUnknownHeader is returned when it's not possible to decode the
+// provided string into a libp2p public key type.
+var ErrUnknownHeader = errors.New("could not decode unknown header")
+
+// ErrUnknownKeyType is returned when value provided is not a valid
+// libp2p public key type.
+var ErrUnknownKeyType = errors.New("could not encode unsupported key type")
+
+var (
+	decMap = headerToKeyType()
+	encMap = keyTypeToHeader()
+)
+
+// Decode returns either the pb.KeyType associated with the provided Header
+// or an error.
+//
+// Currently, only the four key types supported by the [go-libp2p/core/crypto]
+// library are supported.
+//
+// [go-libp2p/core/crypto]: github.com/libp2p/go-libp2p/core/crypto
+func Decode(header []byte) (pb.KeyType, error) {
+	keyType, ok := decMap[string(header)]
+	if !ok {
+		return -1, fmt.Errorf("%w: %s", ErrUnknownHeader, header)
+	}
+
+	return keyType, nil
+}
+
+// Encode returns either the header associated with the provided pb.KeyType
+// or an error indicating the header was unknown.
+//
+// Currently, only the four key types supported by the [go-libp2p/core/crypto]
+// library are supported.
+//
+// [go-libp2p/core/crypto]: github.com/libp2p/go-libp2p/core/crypto
+func Encode(keyType pb.KeyType) ([]byte, error) {
+	header, ok := encMap[keyType]
+	if !ok {
+		return nil, fmt.Errorf("%w: %s", ErrUnknownKeyType, keyType.String())
+	}
+
+	return []byte(header), nil
+}
+
+func keyTypeToHeader() map[pb.KeyType]string {
+	const rsaSigLen = 0x100
+
+	return map[pb.KeyType]string{
+		pb.KeyType_RSA: header(
+			Prefix,
+			multicodec.RsaPub,
+			multicodec.Sha2_256,
+			rsaSigLen,
+			multicodec.DagCbor,
+		),
+		pb.KeyType_Ed25519: header(
+			Prefix,
+			multicodec.Ed25519Pub,
+			multicodec.DagCbor,
+		),
+		pb.KeyType_Secp256k1: header(
+			Prefix,
+			multicodec.Secp256k1Pub,
+			multicodec.Sha2_256,
+			multicodec.DagCbor,
+		),
+		pb.KeyType_ECDSA: header(
+			Prefix,
+			multicodec.Es256,
+			multicodec.Sha2_256,
+			multicodec.DagCbor,
+		),
+	}
+}
+
+func headerToKeyType() map[string]pb.KeyType {
+	out := make(map[string]pb.KeyType, len(encMap))
+
+	for keyType, header := range encMap {
+		out[header] = keyType
+	}
+
+	return out
+}
+
+func header(vals ...multicodec.Code) string {
+	var buf []byte
+
+	for _, val := range vals {
+		buf = binary.AppendUvarint(buf, uint64(val))
+	}
+
+	return string(buf)
+}