Jon Callas

865 reputation

bio	website	callas.org/jon
	location	Hilbert Space
	age
visits	member for	1 year, 3 months
	seen	Dec 15 '12 at 1:46
stats	profile views	18

Cryptographer. Co-author of OpenPGP, DKIM, syslog-sign, ZRTP, the Skein hash function, Threefish cipher, and other things.

Businessman. Co-founder of PGP Corporation, Silent Circle, World Benders, and others. Presently CTO at Entrust.

Software engineer. Worked at the above as well as Apple, DEC, NASA, and others.

	865 reputation	bio	website	callas.org/jon	visits	member for	1 year, 3 months
13 badges		location	Hilbert Space		seen	Dec 15 '12 at 1:46

summary answers questions tags badges favorites bounties reputation activity

8 Comments

suggestions reviews revisions comments badges posts accepts all

Oct 24	comment	Could the Enigma algorithm be classified as a Feistel network? Stream ciphers operate on characters, or arguably even bits in a stream. For Enigma, it's characters. Binary ones like Lorentz or RC4 can be thought to work on bits. Engima takes a character, rattles it around a path and it goes to another character map. (And the wheels ratchet one place.) Computer stream ciphers are a PRNG that is XORed onto the plaintext to yield ciphertext. Block ciphers take a binary block and the key giving another block. That's it. We use chaining modes to encrypt more than one block, but it works on blocks. It is a mapping of input blocks of bits to output blocks.
Aug 21	comment	Are there hash algorithms with variable length output? Actually, the SHA-3 schedule is "by the end of 2012" so it's about where one would expect.
Jun 19	comment	What algorithm does PGP use to encrypt email? I wouldn't point to pgpi.org. It's over a decade out of date and not maintained. But great answer. -- Jon
Jun 19	comment	OpenPGP Signature Packet hashed data You guys have it sorted out, it seems. You're right, it's sometimes difficult to describe code in English. -- Jon
May 15	comment	Is it fair to assume that SHA1 collisions won't occur on a set of <100k strings No, no one has found a way to implement Manuel's 2^51 attack. For that matter, no one has answered my question, "2^51 whats?" 2^51 clock cycles is not very long, and 2^51 years is. Yet both have a work factor of 2^51. (By the way, this is why work factor is a slippery concept.)
Apr 3	comment	Can you make a hash out of a stream cipher? Carter-Wegman MACs are okay for making authenticated encryption, but they're not successful for fast, secure hash functions. As Jalaj points out, there's a different set of security requirements.
Mar 14	comment	Predicting values from a Linear Congruential Generator I've added in more text along with a link to an applicable paper.
Mar 14	comment	Is it safer to generate your own Diffie-Hellman primes or to use those defined in RFC 3526? Thank you for the clarification, poncho. I was trying not to get into the details, but the gist of it. But you are correct, I should have been more weasely.