Hashing algorithms are used to secure passwords by taking the plaintext password, passing it through the cryptographic hash algorithm, and then storing the resulting digest, rather than the plaintext password itself. That way, if attackers are able to compromise the database of passwords, what they get are the hashes and not the actual passwords.
However, the algorithms used to hash passwords in most cases are functions such as SHA-1 and MD5, which have known weaknesses that open them up to brute-force attacks. So if an attacker is able to access a database of hashed passwords, he may be able to crack them, given enough time and compute power. When these algorithms were designed years ago, the hardware needed to crack a hash produced by one of them was not commonly available. But now, powerful GPUs and FPGAs are widely available and can be used by an attacker to crack hashes relatively quickly.
"Password hashing is important because it's where we have a problem. NIST has given us some great standard hashing algorithms. The problem is that these hashes aren't necessarily designed for the specific problem of password hashing — where you need something that's fast enough to hash on a server at login time, but slow enough that a GPU can't crack ten million of them," Green said.