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POWhat is the key size for PBEWithMD5AndTripleDES?
 

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  1. POWhat is the key size for PBEWithMD5AndTripleDES?
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    <p>I am trying to replace PBEWithMD5AndDES with PBEWithMD5AndTripleDES in existing code. So far, I am using the same passphrase that I was using before, and receiving this Exception:</p> <p>java.security.InvalidKeyException: Illegal key size</p> <p>I looked online and saw that DES uses a 64 bit key and TripleDES uses a 128 bit key. I am not clear on the details of how my passphrase is used to generate a key, and not sure where to look to understand this fully. My passphrase is 260 characters long. I tried doubling the length, but I get the same Exception.</p> <p>I am generating a PBEKeySpec from my passphrase, with an 8 byte salt and an iteration count of 12. I see that there's another constructor that takes a keyLength argument, but the documentation describes it as "to be derived," and I don't understand that. I have the idea that I need to modify the iteration count and/or supply a keyLength argument, but I don't want to just do this blindly without fully understanding what I am doing.</p> <p>Here is the basic outline of the code I'm currently using:</p> <pre><code>String passphrase = ... byte[] salt = ... int iterationCount = 12; String algorithm = "PBEWithMD5AndTripleDES"; KeySpec keySpec = new PBEKeySpec(passPhrase.toCharArray(), salt, iterationCount); SecretKey key = SecretKeyFactory.getInstance(algorithm).generateSecret(keySpec); Cipher cipher = Cipher.getInstance(key.getAlgorithm()); AlgorithmParameterSpec paramSpec = new PBEParameterSpec(salt, iterationCount); cipher.init(Cipher.ENCRYPT_MODE, key, paramSpec); byte[] encoded = cipher.doFinal(data); </code></pre>
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      1. POWhat is the key size for PBEWithMD5AndTripleDES?
      1. USBartosz Jakubowski
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    1. COTripleDES, or more specifically DESede uses either a DES ABA key or a DES ABC key. In the 16 byte / 128 bit version, which has an entropy of 112 bit and an effective length of about 80 bit, the first 8 bytes are the first key (A), and the next 8 bytes are the second key (B), then DESede is C = E(Sa, D(Sb, E(Sa, data block))). It's more likely that Oracle uses ABC keys (24 byte, 192 bits, 168 bit entropy, 128 bit effective) because that was the only one they supported for quite some time. 16 byte keys would give an InvalidKeySize, or a InvalidKeySpec exception, if I'm not mistaken.
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      1. POWhat is the key size for PBEWithMD5AndTripleDES?
      1. USMaarten Bodewes
    2. COJust a note: Consider to use AES instead of (Triple)DES - it is both faster and considered more secure.
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      1. USPaŭlo Ebermann
 

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