Digital Signatures

The IT Act 2000 defines a digital signature to mean authentication of an electronic record by a person in whose name the digital signature certificate is issued by means of an electronic method. These certificates are essential for establishing whether the public key belongs to the purported owner and if a competent authority has attested the certificate information.

Through the digital signature, the recipient of a message conforms to the sender of a message that the message is intact and as it was sent. Digital signature is the encrypted message that is appended to a document that in turn confirms the identity of the sender and the integrity of the document. Digital signatures are based on a combination of public key encryption and a one way function that converts a message of any length into a fixed length message digest known as hash function .

is unique for the hashed data. Any change in the data, even deleting or altering a single character, results in a different value. The content of the hash data cannot be, for all practical purposes, deduced from hash which is why it is called 'one way.' The encrypted hash, along with other information, such as the hashing algorithm, is known as a digital signature. A 'distilled version' of the message to be signed is created using hash function and then the hash output is encrypted to generate digital signature. The hash function takes an input message of arbitrary length and output a fixed length code. The algorithm that is considered cryptographically suitable for a hash function should possess consistency, randomness, uniqueness and be unidirectional. Some of the most commonly used Hash algorithms are: Message Digest 4(MD4), Message Digest 5 (MD5) and Secure Hash Algorithm (SHA).

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