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seen Apr 13 at 13:25

Mar
29
comment Cryptographic system with double keys with reversible order
Thank you for your answer! Could you provide any papers on the protocol you've described? Like, if it's secure, why isn't it widespread?
Mar
29
comment Generating shared secret random permutation
Thank you very much for your help! One last question — am I free to split value into left and right halves arbitrarily, or swap left and right halves? If yes, can I just select arbitrary bitmask and do something like (left_half & mask) + ((right_half & ~mask) * seed)?
Mar
28
comment Generating shared secret random permutation
and if doing left_half + (right_half * seed), is it really enough? E.g. isn't that too simple? And what size of finite field should I use? Sorry for dumb questions.
Mar
28
comment Generating shared secret random permutation
well... did I understand you correctly that using cryptographic hash function will also work, but it's just less efficient compared to pure GF math? I'm afraid I'll horribly fail with implementing it myself, just because I know nothing about this field of math, and that's why I'd prefer at least use widely known algorithm.
Mar
28
comment Generating shared secret random permutation
I've read your answer several times, and now I hope I mostly understood it. To your opinion, is Extract(value, seed) := SHA256(seed:value) with seed being at least 512 bit, applicable?
Jun
10
comment Is symmetric key encrypted with server's public key secure
Thank you for full and comprehensive answer!
Jun
8
comment Is symmetric key encrypted with server's public key secure
When Alice first meets Bob, she has to tell him her random chosen persistent secret for Bob to recognize her later - like registration. Bob assumes nothing about Alice upon their first meet. Alice cannot use DH due to MITM threat, so she sends her secret encrypted by Bob's public key - and the only way Mallory could interfere with this is to "register" herself too, without getting access to Alice-Bob communication. They don't use the same session key derived from Alice's secret because I've thought it's safer to choose random key each time.
Jun
8
comment Is symmetric key encrypted with server's public key secure
@HennoBrandsma, yes, in original draft authentication is based on shared secret, so if channel is secure, in most trivial case Alice could just send Bob plaintext password. Mallory does not know Alice's random symmetric session key, as it was encrypted for Bob only. If Mallory forges Alice request to hold her key instead of Alice's, Mallory won't be able to forward Bob's response back to Alice, as she does not know original key. Mallory is also unable to obtain shared secret told by Alice to Bob by listening, as it's encrypted by random symmetric key, which Mallory was unable to retrieve.
Dec
6
comment Speeding up partially known plaintext preimage recovery attack on MD5
Sad to admit you both are completely right, so no donuts for me.
Dec
6
comment Speeding up partially known plaintext preimage recovery attack on MD5
I've initially come up with an idea that it's possible to create better (in any definition of "better") algorithm when input is partially known. Please see my question updated for an idea I'm going to implement, but unsure if am I not reinventing the wheel and similar attempt was already done and proven unsuccessful?