adopted aes key-length trigger values

doc/Crypto.md

@@ -40,6 +40,8 @@ AES also prepends a random value to the plaintext. Its size is adjustable by cha
 
 Apart from n2n's plain C implementation, Intel's AES-NI is supported – again, please have a look at the [Building document](./Building.md). In case of openSSL support its `evp_*` interface gets used which also offers hardware acceleration where available (SSE, AES-NI, …). It however is slower than the following stream ciphers because the CBC mode cannot compete with the optimized stream ciphers.
 
+This cipher's different key-sizes are triggered by the length of the user-provided key: 22 characters or less make n2n use AES-128, between 23 and 32 characters lead to AES-192, and 33 or more characters trigger AES-256.
+
 ### ChaCha20
 
 ChaCha20 was the first stream cipher supported by n2n.

src/transform_aes.c

@@ -187,10 +187,11 @@ static int setup_aes_key(transop_aes_t *priv, const uint8_t *password, ssize_t p
   pearson_hash_256(key_mat, password, password_len);
 
   // the length-dependant scheme for key setup was discussed on github:
-  // https://github.com/ntop/n2n/issues/101
-  if(password_len >= 65) {
+  // https://github.com/ntop/n2n/issues/101 -- as no iv encryption required
+  //  anymore, the key-size trigger values were roughly halved
+  if(password_len >= 33) {
     key_size = AES256_KEY_BYTES;       // 256 bit
-  } else if(password_len >= 44) {
+  } else if(password_len >= 23) {
     key_size = AES192_KEY_BYTES;       // 192 bit
   } else {
     key_size = AES128_KEY_BYTES;       // 128 bit