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bio website touset.org
location San Francisco, CA
age 30
visits member for 1 year, 11 months
seen 2 hours ago

Cyclist. Rubyist.


Jun
2
comment How do I produce a stream of secure random numbers from AES-Counter mode?
An exhaustive list would be quite literally impossible. In the spirit of Bruce Schneier's anecdote, I'll give you one concrete attack outside of the scope of implementing AES-CTR correctly. Are you zeroing out the area of the disk that contained the unencrypted data, after you have encrypted it? In the case of an SSD, are you sure you're zeroing out that data (thanks to automated wear-leveling)?
May
31
revised How can one parallelize tasks in CTR-AES for maximum performance?
added 14 characters in body
May
31
comment How can one parallelize tasks in CTR-AES for maximum performance?
$\vert\vert$ is concatenation, $\oplus$ is XOR.
May
31
comment How do I produce a stream of secure random numbers from AES-Counter mode?
The examples given are merely some types of problems an implementation can have while still producing correct inputs and outputs. It is not an exhaustive list. That said, if you are storing this data on an offline host that you seem to believe will be difficult for any kind of attacker to get a foothold on, why exactly are you bothering to encrypt the data? What is your threat model, and what kinds of attackers are you attempting to thwart?
May
29
answered How can one parallelize tasks in CTR-AES for maximum performance?
May
28
comment Uniform distribution/randomness of characters in the sha256 hash?
FYI, the letter/number pairs are just a base-16 representation of bytes (values 0-255). $\mathrm{00}_h = 0_d$, $\mathrm{10}_h = 16_d$, $\mathrm{f1}_h = 241_d$. There is no need to come up with your own (extremely odd) mapping between these bases.
May
28
comment How do I produce a stream of secure random numbers from AES-Counter mode?
As a rough example, what do you intend to do with these secret messages? Transmit them over a network? If so, an attacker on the wire can trivially flip bits in the plaintext, even if they don't know specifically what that plaintext is. The mantra often repeated here is: GPG for storage, TLS for transmission. They aren't perfect or infallible, but they get details right (well past simple application of AES) that you (or I) overwhelmingly likely wouldn't.
May
28
comment How do I produce a stream of secure random numbers from AES-Counter mode?
Implementing cryptography right isn't only about producing the correct outputs for all inputs. There are many operating-system-specific, threat-model-specific, and environment-specific concerns (too many to list) that must also be addressed by any cryptographic implementations that intend to be used seriously. If you're going through the effort of performing this cryptography on an offline host (indicating some importance), why take the backwards step of writing your own version instead of using a well-vetted existing tool or library?
May
26
reviewed Leave Open Why would splitting a password output be better than separate HMACs for encryption/authentication key derivation?
May
26
reviewed Close Symmetric-Key Based authentication
May
25
comment What are the major flaws and limitations of this hash-based stream cipher design?
Why would hashing before XORing necessarily increase security? Using your gut intuition when dealing with cryptography is usually a bad idea — unless you can prove an assertion, you should not assume it.
May
24
comment What are the major flaws and limitations of this hash-based stream cipher design?
@mic_e That process does not authenticate the ciphertext. Just because a plaintext cannot be easily recovered from a ciphertext does not imply that it can't be manipulated in a way to have predictable effects on the ciphertext. Particularly with a XOR-based cipher, where flipping a bit in the ciphertext flips the exact same bit in the plaintext.
May
24
comment What are the major flaws and limitations of this hash-based stream cipher design?
More to the point, why should anyone bother to examine this cipher in the first place?
May
24
comment What are the major flaws and limitations of this hash-based stream cipher design?
To turn your question on its head, what are the advantages? In what way do existing, well-cryptanalyzed ciphers fall short of your needs, and in what way does this improve upon those shortcomings?
May
20
reviewed Close how to use common modulus attack?
May
12
reviewed No Action Needed Initialize the eight working variables SHA256
May
12
reviewed Approve suggested edit on RSA, finding p,q
May
12
reviewed Close RSA, finding p,q
May
9
reviewed No Action Needed Cryptographically secure keyed rolling hash function
May
9
reviewed Close Open source implementations of Symmetric Searchable Encryption and Order Preserving Encryption