title: Pycrypto AES-CTR implementation
body: <p>I am new to python and pycrypto.
  I am trying to implement AES-CTR. To check my program for correct ciphering I tried to use test sequences from NIST SP 800-38A standard (section F.5). But I do not get correct result. What am I doing wrong?</p>
  
  <pre><code>from Crypto.Cipher import AES
  from Crypto.Utils import Counter
  
  CTRkey="2b7e151628aed2a6abf7158809cf4f3c"
  ctr=Counter.new(128, initial_value=int("f0f1f2f3f4f5f6f7f8f9fafbfcfdfeff",16))
  cipherCTR=AES.new(CTRkey, AES.MODE_CTR, counter=ctr)
  print(cipherCTR.encrypt("f0f1f2f3f4f5f6f7f8f9fafbfcfdfeff".decode("hex")).encode("hex"))
  </code></pre>
  
  <p>Result:</p>
  
  <pre><code>0008007df81ad564b9aadd6b883fef16
  </code></pre>
  
  <p>But the expected result (<em>ciphertext</em>) is:</p>
  
  <pre><code>874d6191b620e3261bef6864990db6ce
  </code></pre>