Chirag's Blog: Digital Signature Algorithm (DSA) | Digital Signature Standards (DSS)

Digital Signature Algorithm & Digital Signature Standards

The National Institute of Standards and Technology (NIST) has published Federal Information Processing Standard FIPS 186, known as the Digital Signature Standard (DSS). The DSS makes use of the SHA and presents a new digital signature technique, the Digital Signature Algorithm (DSA). Latest version also incorporates digital signature algorithms based on RSA and on elliptic curve cryptography. Let us discuss RSA and DSS Approach….

The RSA Approach

In the RSA approach, the message to be signed is input to a hash function that produces a secure hash code of fixed length. This hash code is then encrypted using the sender’s private key to form the signature. Both the message and the signature are then transmitted. The recipient takes the message and produces a hash code. The recipient also decrypts the signature using the sender’s public key. If the calculated hash code matches the decrypted signature, the signature is accepted as valid.

Figure: RSA Approach

The DSS Approach

The DSS approach also makes use of a hash function. The hash code is provided as input to a signature function along with a random number k, generated for this particular signature. The signature function also depends on the sender’s private key (PR_a), and a set of parameters known to a group of communicating principle. We can consider this set to constitute a global public key (PUG). The result is a signature consisting of two components, labelled s and r. At the receiving end, the hash code of the incoming message is generated. The signature is input to a verification function. The verification function also depends on the global public key as well as the sender’s public key (PU_a), which is paired with the sender’s private key. The output of the verification function is a value that is equal to the signature component r, if the signature is valid. The signature function is such that only the sender, with knowledge of the private key, could have produced the valid signature.