Paper 2004/304
Second Preimages on n-bit Hash Functions for Much Less than 2^n Work
John Kelsey and Bruce Schneier
Abstract
We provide a second preimage attack on all $n$-bit iterated hash functions with Damgard-Merkle strengthening and $n$-bit itermediate states, allowing a second preimage to be found for a $2^k$-message-block message with about $k \times 2^{n/2+1}+2^{n-k+1}$ work. Using SHA1 as an example, our attack can find a second preimage for a $2^{60}$ byte message in $2^{106}$ work, rather than the previously expected $2^{160}$ work. We also provide slightly cheaper ways to find multicollisions than the method of Joux. Both of these results are based on expandable messages--patterns for producing messages of varying length, which all collide on the intermediate hash result immediately after processing the message. We also provide algorithms for finding expandable messages for a hash function, using only a small multiple of the work done to find a single collision in the hash function.
Note: Fixed typos
Metadata
- Available format(s)
-
PDF
- Category
- Secret-key cryptography
- Publication info
- Published elsewhere. Unknown where it was published
- Keywords
- hash functions
- Contact author(s)
- john kelsey @ nist gov
- History
- 2004-11-29: revised
- 2004-11-16: received
- See all versions
- Short URL
- https://ia.cr/2004/304
- License
-
CC BY
BibTeX
@misc{cryptoeprint:2004/304,
author = {John Kelsey and Bruce Schneier},
title = {Second Preimages on n-bit Hash Functions for Much Less than 2^n Work},
howpublished = {Cryptology {ePrint} Archive, Paper 2004/304},
year = {2004},
url = {https://eprint.iacr.org/2004/304}
}
