Cryptographic researchers have discovered weaknesses in the encryption algorithms that underpin the security and integrity of electronic signatures.
The issue concerns hash functions - one way mathematical functions that produce a small fixed length string from a much longer message. This is sometimes called a message digest. When two different input values produce the same output value this is called a collision. Teams of researchers have discovered collision in a series of hashing algorithms much more quickly than would be possible using brute-force attacks.
Antoine Joux, of DCSSI Crypto Lab in France, has broken the hash function of the SHA-0 algorithm. Unconfirmed reports from the Crypto 2004 conference suggest a partial break of the more widely used SHA-1 hash function has also been demonstrated. SHA-1 is embedded in popular email encryption programs such as PGP and is also used in SSL browser security.
These findings (still preliminary), and only discovered by using high power computers, mean one type of junk message might be mistaken for another junk message. An attacker's goal would be to substitute something else for the original data and make users trust it. If data can be added to a file (software update or email message) so that the modified message is intelligible and matches the hash of the original message then the impact would be devastating. Things are nowhere near as serious as that.
However, cryptographic weaknesses have been demonstrated. ®