Fix panic when using ed25519 with a key that is not 64 bytes long

crypto.go

@@ -190,6 +190,9 @@ func (s Signer) sign(buff []byte) ([]byte, error) {
 		return ecdsaSignRaw(rand.Reader, &key, hashed[:])
 	case "ed25519":
 		key := s.key.(ed25519.PrivateKey)
+		if len(key) != ed25519.PrivateKeySize {
+			return nil, fmt.Errorf("key must be %d bytes long", ed25519.PrivateKeySize)
+		}
 		return ed25519.Sign(key, buff), nil
 	default:
 		return nil, fmt.Errorf("sign: unknown algorithm \"%s\"", s.alg)

crypto_test.go

@@ -1,6 +1,7 @@
 package httpsign
 
 import (
+	"crypto/ed25519"
 	"crypto/rand"
 	"crypto/rsa"
 	"github.com/lestrrat-go/jwx/v2/jwa"
@@ -100,6 +101,18 @@ func TestSigner_sign(t *testing.T) {
 			want:    nil,
 			wantErr: true,
 		},
+		{
+			name: "ed25519 key not 64 bytes",
+			fields: fields{
+				key: ed25519.PrivateKey(strings.Repeat("a", 63)),
+				alg: "ed25519",
+			},
+			args: args{
+				buff: []byte("abc"),
+			},
+			want:    nil,
+			wantErr: true,
+		},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {