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 Feb27 comment What would a backdoor in symmetric key cipher look like? Yes, the cipher derived from the RSA algorithm would be a stream cipher. (Not sure if that was your question.) Sep10 comment How can I map arbitrary group elements to unique integers without using Hash functions? So, verification of a signature should just consist in trying all public keys, correct? Sep10 comment How can I map arbitrary group elements to unique integers without using Hash functions? I'm not particularly knowledgeable about ring signatures, but couldn't you just release all public keys without disclosing which belongs to whom? Sep10 comment How can I map arbitrary group elements to unique integers without using Hash functions? Sorry, but I remain confused. 1. Why are you keeping the public key secret? 2. What does the third party know? What exactly is it supposed to be able to verify? Sep9 comment How can I map arbitrary group elements to unique integers without using Hash functions? Note that finding $\varphi^{-1}$ might be infeasible in some cases. It would help to know which group you're trying to map to $\mathbb Z_p$. Feb24 comment Difference between Rijndael 128 / 256 blocksize implementations? (and impact of block size in general) @figlesquidge: Uppercase B means bytes, not bits. Jan5 comment Deterministically combine more than one source of entropy I'm not sure I know what you mean. Are you talking about deriving an integer from a pseudo-randomly generated floating point number or about the uniform distribution of the exclusive OR? Jan5 comment Deterministically combine more than one source of entropy The sum of r1 and r2 will have an Irwin–Hall distribution, which is not at all uniform. Dec30 comment Why xor is a linear operation but ordinary adding is not γ1 and γ2 can be any scalar, i.e, any element of the field F. In the example of the 8-bit integers, the only scalars are 0 and 1, yes. But in general, F could be any field, e.g., the set of all rational, real or complex numbers. Dec28 comment Why xor is a linear operation but ordinary adding is not Right, scalar multiplication isn't distributive over field addition. Dec27 comment Using HMAC to secure a “widget” HTTPS encrypts the GET request as well, not just the headers. Dec21 comment Brute Force on 3DES with Reduced Keyspace and Unknown IV Do you anything about the second half of the key (e.g., it consists only of letters) or is it a pseudo-random string? Dec21 comment Brute Force on 3DES with Reduced Keyspace and Unknown IV Do you know which mode of operation has been used? How long is the key? Dec17 comment Scrypt's maximum strength to increase entropy of lame passwords @user4982: You can try to brute-force a password with pretty much every programmable electronic device with enough memory, but the estimated costs of the slides (and paper) use 2002 ASIC technology. Dec17 comment Is there a general method to crack this type of fractionating cipher? How are spaces encoded? Jan4 comment Will length-extension work if secret is not prefixed but appended to the data? No it isn't. But compared to, e.g., HMAC, it suffers from other flaws. See: Why is h(m||k) insecure? Dec20 comment Reason(s) for using a KDF for encryption keys The output of a PBKDF2 implementation may be hexadecimal, but you can convert that output to whatever you want. Although, there are AES implementations that accept hexadecimal keys. Dec20 comment Double Encrypting with two different keys It's important that the keys are actually independent, not just unique. To similar algorithms with related keys could go as far as canceling each other out, resulting in unencrypted plaintext. Dec16 comment Creating a small number from a random octet string @fgrieu: That typo was a byproduct of the edit. Thanks. Which algorithm is the Best is relative. The algorithm provides randomness and is easy to implement, but it generates only 0.79 bits of output for every bit of input. (I assume that's what you mean by odds of failure.) Of course, if $x^2 \leq n$, the algorithm becomes rather inefficient. Dec15 comment Creating a small number from a random octet string @neubert: See comment above.