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6

The modes you are referencing are specifically modes of operations for block ciphers, and therefore are not directly applicable to hash functions. Block cipher operations take 2 inputs, the key and a block-sized input value, and output a block-sized keyed permutation of the input. Hash functions take a variable length input, and output a fixed length value. ...


5

What you are asking is a straight application of Format Preserving Encryption, which builds ciphers which input and output are in a constrained format (generically: common to input and output, hence preserved). The FPE field has many articles with proven techniques; and proposed standards, including BPS and SP800-38G Draft. Note: the method tentatively ...


3

Forget OFB mode. You should use CTR (counter) mode. It has the best bounds, and is parallelizable. This means that when you are using the AES-NI instruction set, encrypt with CTR is about 7 times faster than CBC, OFB etc. If you encrypt in OpenSSL you will get this performance. For a good thorough analysis and comparison of modes of operation, see ...


2

I have a problem with OFB mode, because I have heard that it is stronger than CFB. On the contrary I would say that CFB is stronger. OFB means encrypting the IV again and again to produce the keystream. If you end up in a cycle, the keystream will start repeating itself. (This should not be a practical weakness, but why chance it?) CFB is more like ...



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