Decrypt external AES256/CBC/PKCS7 data with CryptoJS, provided 64-char Hex key from SiteMinder

I'm attempting to using CryptoJS to decrypt a string, provided a 64 character string from SiteMinder.

The decrypted string looks like: 8yi6XwyLPZq%2FNjV9fmoyHYtC2UUS48KlpPLMl063gPwDDLJYkLeUFAwC8hTcXrPJkShbjJTShlLUoh2y17kwOA%3D%3D

And the key provided to me is a 64-character Hex string, like so: B55E3CE5E4E335D61E3224B2EAAA79E68AFF43FFAAA85A9D4F2BA07618DF2D67

After the information is decrypted, it should present a string that shows something like: term1;term2

The JavaScript code I am using to decrypt with CryptoJS looks like: CryptoJS.AES.decrypt( encryptedValue, 64CharacterKeyProvidedAbove ).toString();

However, the decrypted value isn't coming back as expected. I've read some information about providing an IV to use a pre-defined key, but I don't have any information, only the key used when SiteMinder encrypts information from the database it is connected to.

Do I need to change the way I'm using CryptoJS?

Assuming you mean encrypted string looks like 8yi6XwyLPZq%2FNjV9fmoyHYtC2UUS48KlpPLMl063gPwDDLJYkLeUFAwC8hTcXrPJkShbjJTShlLUoh2y17kwOA%3D%3D.

And given that encryption is AES256/CBC/PKCS7.

We can make these observations:

• The string looks URL-encoded and Base64-encoded (%3D is =, and Base64 often ends with =)
• There is no IV which is required for CBC, so it is probably in the first 16 bytes of the encoded string. The remainder of the string is probably the ciphertext

So we can decrypt it with CryptoJS like this:

var encrypted = CryptoJS.enc.Base64.parse(decodeURIComponent(encryptedStr));
var key = CryptoJS.enc.Hex.parse(hexKey);
var iv = CryptoJS.enc.Hex.parse(CryptoJS.enc.Hex.stringify(encrypted).substr(0, 32));
var ciphertext = CryptoJS.enc.Hex.parse(CryptoJS.enc.Hex.stringify(encrypted).substr(32));
var plaintext = CryptoJS.AES.decrypt({ciphertext: ciphertext}, key, {iv: iv});    

Here's a working DEMO on jsFiddle.

Result:

SERLOGINNAME=T6ATD1F;password=QWERTY!8;