c# - AESManaged returns different encrypted value for same key/iv combination -


i found this article online , implemented modified version of it.

public static byte[] encrypt(byte[] input, byte[] iv)     {         var aes = new aesmanaged();          aes.key = stringtobytearray("abcdef1234567890abcdef1234567890abcdef1234567890abcdef1234567890");         aes.iv = stringtobytearray("00010001000000000000000000000000");         aes.keysize = 128;           var encryptor = aes.createencryptor();          using (var ms = new memorystream())         {             using (var cs = new cryptostream(ms, encryptor, cryptostreammode.write))             {                 cs.write(input, 0, input.length);                 cs.close();             }              return ms.toarray();         }     }          public static byte[] stringtobytearray(string hex)     {         var numberchars = hex.length;         var bytes = new byte[numberchars / 2];          (var = 0; < numberchars; += 2)             bytes[i / 2] = convert.tobyte(hex.substring(i, 2), 16);          return bytes;     }

now question have is, here providing same iv , key (obviously testing, in production i'm changing iv each time encrypt), it's returning different encrypted bytes each time encrypt same input.

i looked posts , said output supposed same specific key/iv combination. missing here?

edit:

[testmethod]     public void encryption_returns_same_value_for_same_key_and_iv()     {         const string input = "my input";          var bytes = encoding.utf32.getbytes(input);          var result = encryptionmanager.encrypt(bytes, bytes);         var result2 = encryptionmanager.encrypt(bytes, bytes);          assert.areequal(result, result2);     }

this how i'm calling encrypt method

so after discussion, problem part of code not shown here. indeed, original code above gave same results , unit test should have passed (with additionally using sequenceequal on assertion). however, aes.keysize changed in code (by colleagues) after setting key, this:

aes.key = stringtobytearray("abcdef1234567890abcdef1234567890abcdef1234567890abcdef1234567890"); aes.iv = stringtobytearray("00010001000000000000000000000000");  aes.keysize = 128;

however, found out outputting used key after setting keysize property using

console.writeline("used key encryption: " + bitconverter.tostring(aes.key));

the key changes random key after modify keysize. that's why kept getting different results. sample outputs calling function with same input vector:

used key encryption: c7-35-58-42-3a-2a-79-de-0d-09-78-20-34-90-1f-ec
ciphertext: e4-aa-a3-3b-01-cf-f0-c1-07-9a-0b-73-3e-70-c9-8a

used key encryption: 8a-95-e7-26-60-f9-ce-66-ba-a4-de-d2-fa-70-ac-de
ciphertext: c5-e7-d3-32-38-21-54-25-86-61-70-cb-94-46-a6-37

used key encryption: a4-d7-01-8f-35-2b-7f-2d-e6-0a-a9-7f-95-42-71-d6
ciphertext: f1-b2-75-64-d1-90-75-32-0d-cb-d9-ae-11-ae-db-dd

the problem solved first setting keysize , setting key property itself.


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