435 reputation
18
bio website
location
age
visits member for 8 months
seen Oct 7 '13 at 16:07

Aug
17
comment Are there cryptographic hash functions that can be computed using only paper and pen without leaking any information about the plaintext?
@vyu - if this has a practical application, please explain the environment a bit better: assume that you are in an insecure environment, and try to regenerate your PW. You would do this only in order to get back your private PGP/X.509 keys, and later use those keys to decrypt a ciphertext or deal with clear text. Either the decrypting of the keys using the regenerated PW or subsequent operations require a computer - and no more secrets on that computer, therefore it must be a secured computer. Why can't you also regenerate your hashed PW on that computer? Why only mental PW decryption allowed?
Aug
17
comment Are there cryptographic hash functions that can be computed using only paper and pen without leaking any information about the plaintext?
It is also important to know if the adversary has a use of a computer - in that case, as nightcracker indicated, don't expect any security from this process. If he has only brain+paper, then you may come up with something. I'd say that for any practical PW creation application, it would be much better to spent the alloted time to mentally(+pen-paper) compose a high-entropy PW whithout coming up with a actual mental hashing function which most probably would be a one-shot affair.
Aug
17
comment Are there cryptographic hash functions that can be computed using only paper and pen without leaking any information about the plaintext?
I guess that this an academical assignment whereby the instructor would want you to show your understanding of hashing, secrecy and security in an interesting way. In that case, it requires quite a bit of analytical effort which I doubt you will get it here. Otherwise, I can't see any practical application to your requeirements, since I can't fathom a person doing hours of calculations to come up with a high-entropy PW and still expect to remember all steps after a few weeks, when he wants to regenenerate it. (continued)
Aug
17
awarded  Commentator
Aug
16
answered Any practical uses of machine learning for cryptography?
Aug
15
awarded  Supporter
Aug
14
answered Vulnerabilities if encrypting the same data with 2 different keys
Aug
12
comment AES encryption using a Diffie-Hellman key exchange
@tylo while you come from the cryptographic agorithm point of view, I tried to answer from a application usage point of view. Judging from the question, I take it that the user has a AES encryption application, needs to enter a password, and wonder how to exchange that password with a remote user. I would dare to say that your response, as well as the others here, are too technical for the OP.
Aug
12
answered AES encryption using a Diffie-Hellman key exchange
Aug
11
revised How does certificate-based encryption solve key revocation problem?
added 34 characters in body
Aug
11
answered How does certificate-based encryption solve key revocation problem?
Aug
11
answered Verify Messages to Embedded Device
Aug
10
awarded  Teacher
Aug
9
answered What are the security effects of reusing a public RSA key to encrypt large data by blocks?
Aug
6
comment Achieving 256-bit encryption strength with PBKDF2 - HMAC-SHA1
Now about the inability to increase "entropy" going through a deterministic function - if I judge "entropy" in a sense of a "strength against attack" contained in a password, don't I increase the strength, hence "entropy", by deterministically iterating n times through the hash?
Aug
6
comment Achieving 256-bit encryption strength with PBKDF2 - HMAC-SHA1
@Henrick Thanks you for the formal answer. Regarding your addendum, I am not sure about your claim: The thermodynamic property is very well defined, and a closed thermodynamic system doing work will always have its entropy increased - never staying the same or decreasing. Since there is a "chaotic" element to the natural progression of such systems, cryptographers borrowed that term for their use - but, as you say, "entropy" in the crypto world can go down or stay the same.
Aug
6
awarded  Scholar
Aug
6
accepted Achieving 256-bit encryption strength with PBKDF2 - HMAC-SHA1
Aug
5
comment Achieving 256-bit encryption strength with PBKDF2 - HMAC-SHA1
Thanks for the help and explanation. Your solution will work for me. Sorry that I can't vote you up, but if you post it as an answer, I'd certainly accept it.
Aug
5
awarded  Informed