Stephen Touset

1,251 reputation

215

bio	website	touset.org
	location	San Francisco, CA
	age	29
visits	member for	7 months
	seen	52 mins ago
stats	profile views	14

Cyclist. Rubyist.

	1,251 reputation	bio	website	touset.org	visits	member for	7 months
215 badges		location	San Francisco, CA		seen	52 mins ago

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Apr 8	comment	Does the IV need to be known by AES (CBC mode)? Look at the images. The previous ciphertext block is always used as the "IV" for the next block, both during encryption and decryption. The initialization vector acts as the first "previous block" when none would otherwise be there.
Apr 8	comment	Does the IV need to be known by AES (CBC mode)? This can pretty much be answered trivially by reading the relevant Wikipedia article. Note that attempting decryption without the IV is the logical equivalent of trying to compare a password against a salted hash, without having access to the salt.
Apr 5	answered	Case insensitive verification of HMAC / Base64 signature
Apr 2	awarded	Revival
Apr 2	revised	Is there a practical security difference between XXX-bit encryption? added 197 characters in body
Apr 2	answered	Is there a practical security difference between XXX-bit encryption?
Mar 31	comment	Single-purpose symmetric encryption scheme for single files Interesting. It looks like `EVP_BytesToKey` tries to approximate something like PBKDF2... except the `enc` caller only uses 1 count. facepalm
Mar 30	comment	Single-purpose symmetric encryption scheme for single files @dchest The OpenSSL command line uses PBKDF2 for password-based key derivation. Try again.
Mar 30	comment	Single-purpose symmetric encryption scheme for single files What is the advantage over `openssl enc -aes-128-gcm -in infile -out outfile -k password?
Mar 28	comment	It is reasonably safe to leave a SSH private key with a 30+ character passphrase public? I believe @JohnDeters' point is that your problem is equivalent to a secret sharing scheme with $m = n = 2$. Data derived from the passphrase would constitute one of the two shares, and each server would possess the single remaining share needed to reconstruct the key.
Mar 28	answered	It is reasonably safe to leave a SSH private key with a 30+ character passphrase public?
Mar 28	comment	It is reasonably safe to leave a SSH private key with a 30+ character passphrase public? How can the owning party store the password, then?
Mar 28	comment	It is reasonably safe to leave a SSH private key with a 30+ character passphrase public? Will the RSA key be unlocked and used on those machines? Or will it be transferred to a controlled environment first?
Mar 28	comment	It is reasonably safe to leave a SSH private key with a 30+ character passphrase public? What is the purpose of distributing an RSA private key? Why can't multiple hosts have their own keypair?
Mar 26	comment	which asymmetric cipher provide highest performance? @rsa When in doubt, benchmark on your own hardware with the implementations you have available. If performance is important, nobody can answer this question except for you.
Mar 25	comment	which asymmetric cipher provide highest performance? This can change drastically based on hardware support and the particular implementation you choose. When in doubt, benchmark.
Mar 24	answered	Where can I begin to study the math behind modern cryptography?
Mar 18	comment	How to use GCM mode and associated-data properly Yep, I'm an idiot. The password is the only component that needs to be kept secret.
Mar 18	comment	How to use GCM mode and associated-data properly Sorry, the salt for the password should be kept secret. Not the nonce for encryption.
Mar 18	comment	How to use GCM mode and associated-data properly Those aren't really useful to include. The KDF should be assumed to be collisionless, so the mere fact that they have the key should be sufficient to prove that they know the password and salt. Also, I believe that the AAD should not be used for any data that must be kept secret (which the password and nonce must be).