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How Do I...Generate and compare a hash value?



It is easy to generate and compare hash values using the cryptographic resources contained in the System.Security.Cryptography namespace. Because all hash functions take input of type Byte[], it might be necessary to convert the source into a byte array before it is hashed.

To generate a hash value, create an instance of a hash algorithm and call ComputeHash() on it. The following code creates an instance of the MD5 hash algorithm and calls ComputeHash() on it. The hash function returns a byte array containing the hash value of the byte array Input Byte[] HashVal = (new MD5CryptoServiceProvider()).ComputeHash(Input); Dim HashVal As Byte() = New MD5CryptoServiceProvider().ComputeHash(Input) Byte hashvalue[] = (new MD5CryptoServiceProvider)->ComputeHash(Input);

Note that ComputeHash() is the final operation performed on an instance of a hash object. If another hash value needs to be generated, a new instance of a hash algorithm must be created.

System.Security.Cryptography contains implementations of MD5, SHA1, SHA256, SHA384, and SHA512. The following code computes a SHA1 hash value. Byte[] HashVal = (new SHA1CryptoServiceProvider()).ComputeHash(Input); Dim HashVal As Byte() = New SHA1CryptoServiceProvider().ComputeHash(Input) Byte hashvalue[] = (new SHA1CryptoServiceProvider)->ComputeHash(Input);

To compare hash values, perform an element-by-element comparison of the hash value byte arrays.

Example