refactor to mautrix 0.17.x; update deps

vendor/maunium.net/go/mautrix/crypto/goolm/utilities/main.go

@@ -0,0 +1,23 @@
+package utilities
+
+import (
+	"encoding/base64"
+
+	"maunium.net/go/mautrix/crypto/goolm"
+	"maunium.net/go/mautrix/crypto/goolm/crypto"
+	"maunium.net/go/mautrix/id"
+)
+
+// VerifySignature verifies an ed25519 signature.
+func VerifySignature(message []byte, key id.Ed25519, signature []byte) (ok bool, err error) {
+	keyDecoded, err := base64.RawStdEncoding.DecodeString(string(key))
+	if err != nil {
+		return false, err
+	}
+	signatureDecoded, err := goolm.Base64Decode(signature)
+	if err != nil {
+		return false, err
+	}
+	publicKey := crypto.Ed25519PublicKey(keyDecoded)
+	return publicKey.Verify(message, signatureDecoded), nil
+}