2,606 reputation
525
bio website touset.org
location San Francisco, CA
age 30
visits member for 2 years, 2 months
seen 7 hours ago

Cyclist. Rubyist.


Sep
4
comment Change Salt when Changing Password?
Independent of the rest of the question, salts should always change when a password is changed.
Aug
28
comment Why are some key stretching methods better than others?
Really? Your question here quotes the entire section I removed, asking for clarification of exactly why the given pseudocode has the properties claimed.
Aug
28
comment Repeatable crypto
Also, you may wish to look into the architecture of tarsnap, which was designed to efficiently solve content-aware deduplication of encrypted backups.
Aug
28
comment Why are some key stretching methods better than others?
For what it's worth, I've removed those algorithms from the Wikipedia page. Wikipedia should not be encouraging amateurs to implement their own bespoke key stretching algorithms.
Aug
27
awarded  Nice Answer
Aug
27
comment PBKDF2-SHA256+SHA256 for password storage
That's also possible by storing a random key in the user's cookies and comparing it against the hash of that key in the database. Or by HMACing the session cookie with an in-memory key.
Aug
26
comment PBKDF2-SHA256+SHA256 for password storage
What is gained by tying the session cookie to the user's password in any way?
Aug
26
comment How is SHA1 different from MD5?
With regard to your last statement, what about BLAKE2b? It claims to be faster even than MD5. Is this only due to taking special advantage of modern hardware, or the result of "working smarter, not harder"?
Aug
26
comment PBKDF2 Salt and Password Ordering
That's fair. :) There are a lot of questions here that are thinly-veiled fronts for, "I think I know more than experienced cryptographers, and would like to use preexisting algorithms in strange and confusing ways to increase their security. Is anyone here willing to validate my decisions?" It's useful to weed these types of questions out.
Aug
26
comment What are the advantages of CBC over ECB?
Additionally, clever chosen-plaintext attacks against ECB can reveal plaintexts in $O(n)$.
Aug
26
comment PBKDF2 Salt and Password Ordering
Does it matter? One of these approaches has withstood years of use and examination by cryptographers. The other has not.
Aug
25
revised Found a way to crack AES-128, what now?
edited body
Aug
25
answered Found a way to crack AES-128, what now?
Aug
19
comment Using HMAC-SHA256 with short passwords and sliced outputs for short-lived secure hashing
It doesn't matter what the original hash length was. Trimming the output of a random oracle to $n$ bits will cause it to require $2^{n-1}$ operations on average to find a collision for a particular output, and $2^{n/2}$ operations on average to find any collision.
Aug
17
comment Is my id obfuscation algorithm secure?
Also, you may want to take a second look at asymmetric encryption. Modern ECC like Curve25519 is much faster than RSA, and can be used to derive a shared symmetric secret.
Aug
17
comment Is my id obfuscation algorithm secure?
You can obviously store a unique ID on each chip. Why not store a unique per-chip encryption key using the same mechanism?
Aug
13
comment How is SHA1 different from MD5?
Actually, SHA-1 is on the verge of being considered broken. The best attacks against it find collisions in $O(2^{61})$ operations, rather than the $O(2^{80})$ expected by its output length.
Jul
29
comment Key Derivation from random salted seed, HMAC and HMAC based KDF
@Hashed HMAC is not a magical construct that converts low-entropy inputs into high-entropy outputs. If the system RNG (e.g., /dev/urandom) is providing you with high-entropy randomness, there's nothing further to do. If you only have access to a low-entropy RNG (e.g., C rand), there may be nothing you can do; at absolute best, you can you use a key stretching algorithm like PBKDF2 or scrypt to linearly increase the effective cost of an attacker brute-forcing the key to simulate higher entropy.
Jul
25
comment Idea for user/pass hashing to prevent rainbow tables, would it work?
What advantage does this have over simply generating and storing a random value not derived from the user's password?
Jul
23
comment Which algorithm do you recommend for practical use to generate unique passwords for each website?
Use a password manager to randomly generate your passwords and store them.