mcrypt_decrypt PHP proper usage

Question

I think my PHP intall might have problems. When I try to do this I get Warning: mcrypt_decrypt() [function.mcrypt-decrypt]: Module initialization failed I am writing a small snippet of code that will decrypt the following string encrypted with AES-128 using mode ECB. Key (encoded in base64): aXJhbmRvbXNlY3VyZWtleQ== Encrypted string> (encoded in base64): 3l6xiNdgRG+PkBw5M0lawvJ/fmuTZPRhEcbtqAmOpDI= I keep getting module errors. This is what I have tried: ``` <?PHP $retval = mcrypt_decrypt( "AES-128", base64_decode( "aXJhbmRvbXNlY3VyZWtleQ=="), base64_decode( "3l6xiNdgRG+PkBw5M0lawvJ/fmuTZPRhEcbtqAmOpDI") , "ECB"); echo $retval; ?> ``` here is my relevant phpinfo. I dont see AES-128 . Maybe thats the problem. ``` mcrypt mcrypt support enabled Version 2.5.8 Api No 20021217 Supported ciphers cast-128 gost rijndael-128 twofish arcfour cast-256 loki97 rijndael-192 saferplus wake blowfish-compat des rijndael-256 serpent xtea blowfish enigma rc2 tripledes Supported modes cbc cfb ctr ecb ncfb…

Accepted Answer

You are close, there are 2 small problems.

First, `AES-128` is not a valid cipher constant from mcrypt. AES is really rijndael which you have support for. The mcrypt cipher constant for AES-128 is `MCRYPT_RIJNDAEL_128` which is the string `rijndael-128`. Second, the mcrypt mode must be lowercase.

Changing your code to:

```
<?php
$retval = mcrypt_decrypt( "rijndael-128",
    base64_decode( "aXJhbmRvbXNlY3VyZWtleQ=="), 
    base64_decode( "3l6xiNdgRG+PkBw5M0lawvJ/fmuTZPRhEcbtqAmOpDI") ,
    "ecb");

echo $retval;
```

yields the correct output of: `Is 3 random enough?`

Personally, I'd go with the mcrypt constants rather than the actual strings, so replace `rijndael-128` with `MCRYPT_RIJNDAEL_128` and `ecb` with `MCRYPT_MODE_ECB`.

On a side note, consider using CBC with an IV instead of ECB if you are encrypting lots of sensitive information.

Mcrypt can easily create IVs for you with the proper lengths. Sample code:

```
$ivsize = mcrypt_get_iv_size(MCRYPT_RIJNDAEL_128, MCRYPT_MODE_CBC);
$iv     = mcrypt_create_iv($ivsize);
```

Use this IV when encrypting and decrypting. You can pass the IV along with your data as a base64 encoded string for portability.

mcrypt_decrypt PHP proper usage

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