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comment Turning a 64 bit block cipher into a 128 bit block cipher
Almost. It's a Feistel network, except that you encrypt the left half with the right half as the tweak, instead of using a PRF-then-XOR approach. See the left side of Figure 5 of the linked PDF (pg 11). You'll only get a q^2/2^64 security bound, though. (If you were to start with a TBC that had beyond-birthday-bound security, you could instead use a three-round Feistel construction to avoid this problem. But this would probably be far too slow).
Jun
19
comment Turning a 64 bit block cipher into a 128 bit block cipher
The same paper shows that you can construct a 2n-bit TBC out of an n-bit TBC using two rounds, which might be the answer @Maarten_Bodewes is looking for (since a TBC can be used as a traidtional blockcipher). So that works out to be two blockcipher calls plus two 64-bit finite field operations (assuming LRW) or four blockcipher calls (assuming XEX).
Jun
11
revised How is an epsilon of 1/1000 non-negligible?
added 343 characters in body
Jun
11
revised How is an epsilon of 1/1000 non-negligible?
added 343 characters in body
Jun
11
revised How is an epsilon of 1/1000 non-negligible?
added 1 character in body
Jun
11
revised How is an epsilon of 1/1000 non-negligible?
added 1 character in body
Jun
11
answered How is an epsilon of 1/1000 non-negligible?
May
31
reviewed Leave Open Operation modes of block ciphers how are used?
May
27
reviewed Close Why is public key cryptography not widely used in governments?
May
27
reviewed Reviewed Is HMAC-MD5 still secure for commitment or other common uses?
May
27
reviewed No Action Needed Why is public key cryptography not widely used in governments?
May
25
comment How many bits of entropy can I expect from /dev/urandom in iOS?
Once you've collected, say, 256 bits of entropy, you can use that to generate essentially arbitrary amounts of pseudorandom bits that are secure for all practical purposes. CTR_DRBG is a perfectly good way to go about doing this. Concerns over "running out" of entropy are misplaced. Others have put it more elegantly than I can: gist.github.com/tarcieri/6347417, sockpuppet.org/blog/2014/02/25/safely-generate-random-numbers
May
24
reviewed Close Executing encrypted code?
May
24
reviewed Approve perfect-secrecy tag wiki excerpt
May
24
reviewed Approve error-propagation tag wiki excerpt
May
24
reviewed Approve memory-hard tag wiki excerpt
May
23
comment Encrypt-Mix-Encrypt: Full Diffusion?
There were originally some patent issues (which may or may not have been resolved since, I haven't seen anything definitive). Additionally, EME requires two blockcipher calls per block of input, which slows performance.
May
23
answered Encrypt-Mix-Encrypt: Full Diffusion?