diff --git a/libretroshare/src/util/i2pcommon.cpp b/libretroshare/src/util/i2pcommon.cpp
index 0733a807d..524219eb3 100644
--- a/libretroshare/src/util/i2pcommon.cpp
+++ b/libretroshare/src/util/i2pcommon.cpp
@@ -50,8 +50,10 @@ std::string publicKeyFromPrivate(std::string const &priv)
 	 * https://geti2p.net/spec/common-structures#keysandcert
 	 * https://geti2p.net/spec/common-structures#certificate
 	 */
-	if (priv.empty() || priv.length() < 884) // base64 ( = 663 bytes = KeyCert + priv Keys)
+	if (priv.length() < privKeyMinLenth_b64) {
+		RS_WARN("key to short!");
 		return std::string();
+	}
 
 	// creat a copy to work on, need to convert it to standard base64
 	auto priv_copy(priv);
@@ -163,8 +165,10 @@ std::string publicKeyFromPrivate(std::string const &priv)
 
 bool getKeyTypes(const std::string &key, std::string &signingKey, std::string &cryptoKey)
 {
-	if (key.length() < 522) // base64 (391 bytes = 384 bytes + 7 bytes = KeysAndCert + Certificate)
+	if (key.length() < pubKeyMinLenth_b64) {
+		RS_WARN("key to short!");
 		return false;
+	}
 
 	// creat a copy to work on, need to convert it to standard base64
 	auto key_copy(key);
diff --git a/libretroshare/src/util/i2pcommon.h b/libretroshare/src/util/i2pcommon.h
index 0a76fa080..f0da0322b 100644
--- a/libretroshare/src/util/i2pcommon.h
+++ b/libretroshare/src/util/i2pcommon.h
@@ -186,6 +186,39 @@ static const std::array<std::pair<uint16_t, uint16_t>, 12> signingKeyLengths {
 	/*SigningKeyType::RedDSA_SHA512_Ed25519  */ std::make_pair<uint16_t, uint16_t>( 32,  32),
 };
 
+/*
+ * Key length infos:
+ *
+ * BOB private key
+ * len b64: 884
+ * len pln: 663
+ *
+ * BOB public key / destination
+ * len b64: 516
+ * len pln: 387
+ *
+ * SAMv3 private key
+ * len b64: 908
+ * len pln: 679
+ *
+ * SAMv3 public key
+ * len b64: 516
+ * len pln: 387
+ *
+ * Example:
+ * in bytes, public key only
+ *   384 (Key) + 3 (Null certificate) = 387 bytes
+ *   384 (Key) + 7 (key  certificate) = 391 bytes
+ *
+ * in bytes public + private key
+ *   384 (Key) + 3 (Null certificate) + 256 (ElGamal) + 20 (DSA_SHA1) = 663 bytes
+ *   384 (Key) + 7 (key  certificate) + 256 (ElGamal) + 32 (EdDSA_SHA512_Ed25519) = 679 bytes
+ */
+constexpr size_t pubKeyMinLenth_b64 = 516;
+constexpr size_t pubKeyMinLenth_bin = 387;
+constexpr size_t privKeyMinLenth_b64 = 884;
+constexpr size_t privKeyMinLenth_bin = 663;
+
 /**
  * @brief makeOption Creates the string "lhs=rhs" used by BOB and SAM. Converts rhs
  * @param lhs option to set