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I'm looking at downloading the C# binary for Bouncy Castle and see two downloads with source code. One has the IDEA algorithm, the others presumably not.

http://www.bouncycastle.org/csharp/

Why make separate distributions?

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1 Answer 1

up vote 6 down vote accepted

In some countries, IDEA is patented and redistributing an implementation of it requires it to be licensed. IDEA was a default cipher used in early versions of PGP. For backward compatibility, it is included in OpenPGP which Bouncy Castle implements.

For your case (a new application), get the distribution without it and use AES instead.

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And the IDEA patent expires in 2012. Just be patient ! Anyway, IDEA uses 64-bit blocks, which is not good if trying to encrypt gigabytes of data; a cipher with 128-bit blocks should be used instead, e.g. AES. –  Thomas Pornin Jan 20 '11 at 13:13

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