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I am totally new to encryption, so this question might be trivial - however, I had to google for 2 hours to understand even the basic terms, so bear with me.

The string I need to send is a Base64 Encoded String of an encrypted JSON object. Here's the spec they sent me:

  • Encryption Method: Rijndael
  • Cipher Mode: CBC
  • Padding Mode: PKCS7
  • We will provide you with a custom Base64Encoded Key and IV.

I checked out crypt's Rijndael algorithm, but I don't see where to plug the IV into... Not sure if CBC and PKCS7 are default - if they aren't, I don't know how to change these either...

So:

  • Can be crypt easily modified to support this stuff?
  • Maybe it does support it already as-it-is, just my total lack of cryptographic knowledge doesn't allow for a proper use?
  • If neither of the above, is it possible to do this in Ruby?
Peter Szinek
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2 Answers2

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I pretty much doubt they really use Rijndael. They likely use AES (which is is subset of Rijndael with fixed 128 bits block size and only three standardized key size (128,192 and 256 bits)). Without them supplying blocksize and keysize you cannot be sure anyway, you can likely assume AES-128, but their spec is incomplete at best.

The IV is not related to the cipher algorithm but to the chaining mode, in your case CBC.

AES, CBC, PKCS7 are available in Ruby via OpenSSL, shouldn't be too much trouble.

Edit: people thinking they use Rijndael make me think they use .NET, in which case that question should solve your issues : How to decode Rijndael in ruby (encoded in VB.net)

Community
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Bruno Rohée
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Crypt::Rijndael

This is included in ruby now and can do the decryption of Rijndael easily.

abc123
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