9,417 reputation
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bio website github.com/CodesInChaos
location Frankfurt, Germany
age
visits member for 3 years
seen 27 mins ago

Jun
13
revised GGM PRG construction: Why do we need to change keys all the time with underlying PRG
edited tags
Jun
13
revised How does the birthday attack work in AUTH and UF-CMA games?
edited tags
Jun
13
revised Are there any authoritative definitions of “key stretching”?
edited tags
Jun
13
revised What is difference between PRG, PRF, and PRP
deleted 4 characters in body; edited tags
Jun
13
revised Can one detect if two pairs of elements in Zp have the same exponential relation?
edited tags
Jun
13
wiki created pki description
Jun
13
wiki created pki excerpt
Jun
13
comment Can Poly1305 be used with block ciphers running in CTR mode?
A block cipher in CTR mode is a stream cipher.
Jun
12
comment Why is it impractical to generate a semiprime dictionary?
The problem is that there more than $2^{1000}$ primes that fall into the range of RSA-2048. Totally infeasible to find them all.
Jun
12
comment Algorithm: How to use x and y mouse movement co-ordinates to generate random data?
stuff them all into a crypto hash such as SHA-512.
Jun
11
revised Preimage resistance hash in digital signature
added 27 characters in body
Jun
11
comment length extension attack on an MD5 hash of a text file of about 10K Bytes?
That isn't a length-extension. It's a second-pre-image and totally infeasible (cost above 2^120)
Jun
10
comment When using HMAC, does key encoding matter?
You can't get 512 bits of entropy with HMAC-MD5. The two keys get compressed before use, so they are reduced to 128 bits each. In some situations that might give a combined strength of 256 bits, but in others it won't. There might be meet-in-the-middle attacks, or producing collisions after the first step with 2^64 queries which enable a 2^128 brute-force search against the first key disregarding the second key,... In short I wouldn't rely on HMAC having a larger security level than the hash size.
Jun
9
comment Amateur question: two-way RSA?
1) It's expensive to encrypt all messages with RSA 2) You need to get all the details correct. Replay-attacks,... 3) Exchanging public keys is the hard problem. You need to figure out if the given public key belongs to the party you want to talk to. 4) Good transport encryption protocols offer forward-secrecy. Generating ephemeral RSA keys is a bit annoying compared to diffie-hellman keys.
Jun
9
answered “proof of access” schemes
Jun
9
reviewed Approve suggested edit on How random are commercial TRNGS
Jun
9
comment When using HMAC, does key encoding matter?
IMO using text representations of keys is silly, but it doesn't cause any security issues.
Jun
7
comment Why is TLS SRP verifier based on user name?
The server can choose the salt, so it can start a multi-target attack by giving all users the same salt.
Jun
7
comment Can substrings of a long string be efficiently authenticated?
making leaves smaller than twice the hash size makes little sense. Typically leaves are even bigger than that, for example TTH uses 1KiB leaves.
Jun
7
comment Can substrings of a long string be efficiently authenticated?
Your trivial solution is open to an attack where the attacker picks chunks from different messages that were authenticated with the same key. So if you go that way you need to include a message specific value in the MAC, losing the ability for incremental updates.