MD5 and Sha 1 algorithm - VPN Tutorial
Sha-1 (Secure hash algorithm)
Message integrity algorithms ensure data has not been changed in transit. They use one way hash functions to detect if data has been changed.
Sha-1 (Secure Hash Algorithm), also known as HMAC-Sha-1 is a strong cryptographic hashing algorithm, stronger than MD5. Sha-1 is used to provide data integrity (it is a guarantee data has not been altered in transit) and authentication (to guarantee data came from the source it was suppose to come from). Sha was produced to be used with the digital signature standard.
Sha-1 uses a 160-bit encryption key. It is cryptographically stronger and recommended when security needs are higher.
Cryptology specialists did announce a possible small mathematical weakness in Sha-1 and as a result Sha-2 was made available. Sha-2 is actually a group of algorithms, which consist of Sha-256, Sha-384 and Sha-512. However Sha-1 has proven to be a strong hashing algorithm and no records of it being hacked so far.
Other integrity algorithms include MD2, MD5, MD6, Haval and Tiger.
Wikipedia's guide to Sha-1