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Nov
21
comment Is storing the hash of a key together with ciphertext encrypted with that key secure?
@StephenTouset, agreed, good point! If that's the issue, then my proposal should be combined with your proposal: store a UUID that uniquely identifies the key together with the ciphertext. Let's hope that user4328 returns to clarify the nature of his/her requirements.
Nov
21
revised Is storing the hash of a key together with ciphertext encrypted with that key secure?
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Nov
21
answered Is storing the hash of a key together with ciphertext encrypted with that key secure?
Nov
21
revised Is storing the hash of a key together with ciphertext encrypted with that key secure?
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Nov
20
answered Proof that a function constructed from a PRP is, or is not a PRF?
Nov
20
comment Will varying plaintext compensate for a fixed initialisation vector?
@Brent.Longborough, The answer will probably depend upon specifics, such as exactly how much known plaintext the attacker has. But in any case, this may be getting too far off-base to explain in a comment thread, so maybe you'll need to post a second question. Sorry about that. Or you could just take it as a bottom line: it's gonna be safer to prepend with a random 16-byte IV, even if you're using 8-bit CFB mode (with a constant IV).
Nov
20
comment detecting ROT13/base64 encryption
What's wrong with just decrypting it and checking that the result looks reasonable? That's a perfectly valid method of detecting those schemes. In particular, that is one example of an algorithm that tests the ciphertext and tells YES if it is ROT13/Base64 (or NO if it isn't).
Nov
20
comment Will varying plaintext compensate for a fixed initialisation vector?
@Brent.Longborough, 8-bit CFB mode is better; it'll probably reveal only the first 8-24 bits of the PAN or so. It might be a bit more than 8 bits. Say you have ten million records in the database. Then there will be one million records whose PAN starts with, say, 3, and these can all be identified. Thanks to how 8-bit CFB mode works, the second digit of the PAN will be encrypted by xor with a constant (this constant depends upon only the first digit of the PAN), so it may be possible to decrypt those 2nd digits too. (You can certainly identify the PANs that start with 38 or 39.)
Nov
20
revised Will varying plaintext compensate for a fixed initialisation vector?
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Nov
20
revised Is there an authenticated encryption scheme where the recipient can attribute the message to a single sender?
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Nov
20
answered Is there an authenticated encryption scheme where the recipient can attribute the message to a single sender?
Nov
20
revised Is there an authenticated encryption scheme where the recipient can attribute the message to a single sender?
clarify that this is not about non-repudiation, as Robert I. later explained in his comments to my answer
Nov
20
revised Is there an authenticated encryption scheme where the recipient can attribute the message to a single sender?
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Nov
20
revised Will varying plaintext compensate for a fixed initialisation vector?
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Nov
20
comment Will varying plaintext compensate for a fixed initialisation vector?
I made major revisions. I think they improve things, but CodesInChaos, I encourage you to look over them yourself and see whether you agree or not.
Nov
20
revised Will varying plaintext compensate for a fixed initialisation vector?
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Nov
19
revised Will varying plaintext compensate for a fixed initialisation vector?
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Nov
19
revised Will varying plaintext compensate for a fixed initialisation vector?
Explain a bit more.
Nov
19
revised Will varying plaintext compensate for a fixed initialisation vector?
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Nov
19
answered Will varying plaintext compensate for a fixed initialisation vector?