3,156 reputation
618
bio website ripple.com
location Northern California
age 44
visits member for 2 years, 8 months
seen Mar 15 at 23:00

I am Chief Cryptographer at Ripple Labs (formerly OpenCoin) and one of the architects of the Ripple payment system.


Feb
18
comment Is it possible to generate an RSA SHA1 signature only from a public key?
What would be the point of a signature that anyone could make? What purpose would it serve?
Feb
18
comment Why is RSA encryption significantly faster than decryption?
I just benchmarked OpenSSL and the ratio was around 14 to 1.
Feb
15
comment Encrypting a key with the same key
@madhukar2k2: No, that would not make the system insecure. If you pick a random 128-bit number, you might pick zero, and an attacker might start searching at zero. But if you exclude zero as "insecure", then an attacker doesn't have to start at zero and the problem repeats for one. You only want to exclude unsafe choices if they have a high enough probability that the benefit from excluding them exceeds the cost. Reducing the search space by excluding a matching key has a cost (reducing an attacker's search space) greater than the benefit (eliminating one unsafe random key).
Feb
15
comment Encrypting a key with the same key
This question makes no sense. You're asking us why something would be insecure without telling us why you want to do it. Something can't be insecure unless there's something you're trying to prevent that would constitute a security failure. Without requirements whose violation would constitute a security problem, it's logically impossible for something to be "insecure".
Feb
13
comment Is signing a hash instead of the full data considered secure?
The great thing about standards is that there are so many to choose from.
Feb
13
comment md5: is reverse length-extension attack possible?
It is important to understand that Merkle–Damgård hashes were never designed to resist attacks of this type. Any properties like this that they have are just the result of pure luck.
Feb
13
answered Is signing a hash instead of the full data considered secure?
Feb
9
comment Is Convergent Encryption really secure?
@PeterDolberg: You are correct. If you use AES-CBC, the IV has to be derived the same way as the key.
Feb
7
comment How to check the strength of an encryption algorithm?
Your question seems to be confusing two different things. The question itself asks how to check the strength of an algorithm. But the body says you want to check if an application is secure. These are two totally different questions with totally different answers. (And the algorithm has to be known secure before there's a chance the application is secure, so one comes before the other.)
Feb
5
comment Source for examples with broken cryptography
@CodesInChaos: +1. Great link. There are some 10 SHA-3 candidates which were completely broken.
Feb
5
comment Why does the recommended key size between symmetric and assymetric encryption differ greatly?
Short answer: In order to provide comparable levels of security.
Jan
29
comment Same Size Crypto Algorithm?
To 100% clarify, you are looking for an encryption algorithm that maps every possible binary input with an integral number of bytes to a encrypted output of the same length. Is that correct? And you understand the inherent security problems with such an algorithm? (No defense against corruption, replay attacks, and so on.)
Jan
19
comment Is it safe to use RSA as a proof-of-work system?
In the vast majority of realistic applications, any proof of work system can be parallelized simply by requesting many challenges from the server.
Jan
19
comment Is it safe to use RSA as a proof-of-work system?
Another option is to have the server generate two primes and give the client the product of the two primes. The client must factor the product and return the smaller prime.
Jan
19
comment A proof-of-work random number generation system for Pokémon
I think that's a distinction without an actual difference. If it doesn't happen, what difference does it make if it didn't happen because it was impossible or because it was unlikely? If I die without having won the lottery, does it matter to me that it wasn't impossible?
Jan
17
revised What does a “cycle” mean in cryptography benchmarks?
deleted 31 characters in body
Jan
15
answered What does a “cycle” mean in cryptography benchmarks?
Jan
15
answered A proof-of-work random number generation system for Pokémon
Jan
15
answered Is the One Time Pad (OTP) considered a cryptographic hash function?
Jan
15
comment Is the One Time Pad (OTP) considered a cryptographic hash function?
@Woot4Moo: Without a compression function, OTP is not a hash. With any non-trivial compression function, OTP is not just OTP anymore. With a trivial compression function, OTP is not cryptographically secure. But ignoring that, OTP is reversible, so useless as a hash function.