Re:Ledger's Advanced Side Channel Analysis Repository
by jolmg on Tuesday February 19, 2019 @01:52PM
(#19201637)
But if you use cryptographic hash functions, then you can't do the timing attack described because any one character change changes the whole hash.
[ Parent
| on HN ]
Re:Ledger's Advanced Side Channel Analysis Repository
by Nursie on Tuesday February 19, 2019 @02:02PM
(#19201739)
Not for cracking a password perhaps, but imagine you have a system that looks at a MAC'd ciphertext. You want the system to attempt to decrypt a malicious ciphertext you've generated, but it won't until you have passed its MAC check.
With a timing attack, you can iterate the bytes of the MAC, itself probably based on a cryptographic hash like HMAC(sha256), until you get something that gets to the second stage.
You reduce MAC-forging complexity from 2 to the power of the number of MAC bits, to 256 times the number of bytes in the MAC.