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I am a math/computer nerd. Nothing to see here, move along.


1d
comment SHA and “Bits of Security”
It would be simpler to truncate the hash. Also, note that a 128-bit hash digest will only have 64 "bits of security" when it comes to finding collisions, even if it still has 128 "bits of security" when it comes pre-image resistance. That is, an attacker will likely find a collision before trying 2^64 values using a generic Birthday Attack (en.wikipedia.org/wiki/Birthday_attack).
May
17
awarded  Enlightened
May
17
awarded  Nice Answer
May
16
awarded  Yearling
Jan
30
comment How can I allow acces to encrypted data if only 2 out of 3 users provide a secret?
@KarlIvarDahl Much as I appreciate having an answer accepted, I'd encourage you to accept what you feel is the best answer, rather than the first sufficiently okay answer. Everyone benefits more in the long run if the game rewards quality rather than speed (for example, people may reach this question from Google in the future and only bother reading the accepted answer).
Jan
30
revised How can I allow acces to encrypted data if only 2 out of 3 users provide a secret?
added 40 characters in body
Jan
30
awarded  Supporter
Jan
30
answered How can I allow acces to encrypted data if only 2 out of 3 users provide a secret?
Jan
6
comment Help to understand secure connections and encryption using both private/public key in RSA?
May I recommend crypto.stackexchange.com.
Jan
6
comment Help to understand secure connections and encryption using both private/public key in RSA?
It seems we just keep missing each other. I touched on HMACs in my answer. The reason HMAC (as opposed to a simple hash) is necessary is because most encryption algorithms are, to varying degrees, malleable. That is, they'll stop Eve from learning about the message's contents, but it won't stop her from tampering with the ciphertext in such a way that the decrypted plaintext changes in ways she can control. Your statement that "[the hash] will get garbled when Alice or Bob receive the message and attempt to decrypt it" can actually be false!
Jan
6
awarded  Editor
Jan
6
revised Help to understand secure connections and encryption using both private/public key in RSA?
added 1377 characters in body
Jan
6
answered Help to understand secure connections and encryption using both private/public key in RSA?
Dec
8
comment Is it legal to publish viticim's password and email?
Questions of legality aside, you may want to consider the question of whether it's ethical. Would you be jeopardizing their security? Some may have recycled the compromised password for their emails (or other accounts). What about their privacy? Some people choose embarrassing passwords, and, depending on where the database came from, the fact that they had an account their might be something they don't want published.
Sep
15
comment How does SSL protect against network level attacks on integity?
In CBC mode, an attacker can modify a specific byte at the cost of mangling the preceding block.
Feb
25
awarded  Teacher
Feb
25
answered How can I encrypt something user provided without risk of the key being exposed?
Feb
25
comment How can I encrypt something user provided without risk of the key being exposed?
Length-extension attacks apply to hash functions, not encryption algorithms. Standard encryption algorithms (such as CBC) are secure against chosen-plaintext attacks, so in fact they are explicitly designed to be secure in this type of scenario---the ability to encrypt plaintexts of his choosing does not give an attacker information on other ciphertexts. That being said, you should probably provide some more details on what your service is doing and what your threat model is. Crypto.stackexchange.com is probably a better place to ask this question.