Hendrik Brummermann

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May 6	comment	session keys in an online e-voting system Server1 can just generate a large random number as token and send a list of valid tokens to Server2. Alternatively Server1 can use a HMAC. Please note that this is voting scheme in not in compliance with the requirements of democratic elections for multiple reasons: The voter cannot prevent Server1 and Server2 from cooperating to reveal his vote. Furthermore a voter cannot verify that the counted votes match the actual votes.
May 6	comment	session keys in an online e-voting system The idea behind this concept is to have server1 verify the identity of the person in order to prevent a voter from voting twice. In a real election, this is done by the voting committee. Server1 hands out a token that can be used to vote exactly once, like the empty piece of paper on which you mark your vote. Server2 accept the token and the vote, like the ballot-box.
May 3	comment	recommendation for steganography tool? Hello Layla and welcome to crypto. This side is about the concepts of cryptography. So unfortunately questions about software are off topic here.
Apr 28	comment	Determine the Identity of Caller Hello Matthew and welcome to crypto. Unfortunately your question is off topic here. Normally I would migrate it to Security, but since you already posted it there, I am just going to close it.
Jan 14	comment	Mental Poker with untrusted server (i.e. no peer to peer) Implementing the game using web technology means that the rouge server may send a manipulated program (javascript) to the user. Therefore the user must be able to do the verification without relying on his game client.
Nov 2	comment	What is the most secure encryption algorithm? [JS/PHP] First of all: You need https anyway in order to prevent an attacker from manipulating the JavaScript in transit. Otherwise the modified javascript can just send a plain text copy of the data to another server. AES is a good solution, if you want to prevent the webserver from seeing it (e. g. if the webserver is under the control of an American cloud company which is in violation of European privacy law). While this will prevent passive sniffing on the webserver, an active attack by the webserver will modify the JavaScript.
Oct 30	comment	Why is an Encrypt-and-MAC scheme with deterministic MAC not IND-CPA secure? @IlmariKaronen, there is, but I forgot to select the checkbox. Sorry.
Oct 30	comment	Why is an Encrypt-and-MAC scheme with deterministic MAC not IND-CPA secure? @BiggBen1989 "'Deterministic' simply means that, given the same input, the algorithm always produces the same output. That is, if $m=m'$ and $k=k'$, then $Mac_k(m)=Mac_{k'}(m')$. As for "the MAC part of the message", I simply meant $t$ in the output $(c,t)$ of $Enc'$. (Ps. I've flagged your (non-)answer for the mods to convert to a comment. Hopefully they can move my comment too, but if not, I can just repost it.)" by Ilmari Karonen
Oct 12	comment	What happens to the entropy of a password when you hash it? On the practical side, please do not use MD5 to hash passwords, but a hashing function that is designed for passwords.
Sep 3	comment	Which blind signature schemes exist, and how do they compare? @noone, Google's result list heavily depends on location, language, previous searches and other variables. Please post a direct reference instead of pointing to a random entry on Google.
Aug 29	comment	Finding the LFSR and connection polynomial for binary sequence. Hi jamesj629 and welcome to crypto. Please provide a short summary of the document you linked.
Jul 4	comment	Poor man's SSL - is this method as safe as SSL/TLS? Please give more information on the environment that does not provide a SSL library. You really should try to stick to well tested standards instead of inventing your own crypto.
Jun 30	comment	How are state wiretaps obtaining plaintext from encrypted transmissions? You can add "email stored on the servers of the email providers such a gmail". So while the communication with gmail is encrypted using SSL, the stored mails are not.
Jun 24	comment	How much would it cost in U.S. dollars to brute force a 256 bit key in a year? According to xkcd, $5 for hardware.
Jun 17	comment	Is this password migration strategy secure? Do you mean? `original_salt + bcrypt(MD5(original_salt + password), new_secure_salt)`
Jun 16	comment	Is it possible to use the RSA algorithm, or a variant, for software licensing? Keep in mind that the common way to attack license checks is to patch the conditional jump at the end of the check. So the program will always execute the code path for successful checks.
Jun 15	comment	Assistance Cracking Classical Cipher Hello Eli and welcome to Crypto. There is a word: "If you give a man a fish, you feed him for one night. But if you teach him how to fish, he will be fed for the rest of his life." I think, it will be more helpful, if you explain how your approached the problem instead of spoiling the solution. But congratulations for finding it.
Jun 12	comment	Looking for cipher that uses one ciphertext @Globalnomad, yes, he can see at least the number of other entries.
Jun 11	comment	What's the reason for applying the hash twice when hashing with salt? LinkedIn did not know the `secret`, they only knew `hash_without_salt(secret)`. That's what they stored in their database. So unless they waited for every person to login, the only way to add a salt, is to take the stored unsalted hash as input.
Jun 10	comment	What is the difference between known-plaintext attack and chosen-plaintext attack? +1, but xor is the standard example for known-plaintext based attacks: `cyphertext = key xor plaintext` implies `key = plaintext xor cyphertext`.