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What is a digital signature?

About Digital Signature

– Digital signature plays an important role in the field of cryptography.
– It is used in digital certificates.
– It can be defined as a mathematical scheme used in the demonstration of the authenticity of a document or a digital message.
– A digital signature is included so that the receiver can trust the message sent by its owner.
– The digital signature ensures that the person who has sent message cannot deny sending it (this includes non – repudiation and authentication) and also that there was no tampering done to message during its transition (i.e., the integrity of message is preserved.).

Applications of Digital Signature

Some applications of digital signature are:

  • Software distribution
  • Financial transactions
  • Detection of tampering or forgery

– The most common use of the digital signatures is in the implementation of the electronic signatures.
– Electronic signatures refer to the any type of electronic data concerned with a signature.
– However, digital signatures are not used by all the electronic signatures.
– Electronics have got a legal significance in countries such as U.S., members of European Union and India.
– Asymmetric cryptography is employed by the digital signatures.
– Some channels are non-secure, when messages are sent over such channels, receivers find it hard to trust the message i.e., whether it is from the known source.
– However, if in the same message digital signature is included it assures the recipient that the message has been sent by the trusted source.
– Digital signatures are considered to be equivalent of the handwritten signatures that are traditionally used in a number of respects.
– However, it is pretty easy to forge the handwritten signatures but if the digital signatures are properly implemented, they cannot be forged so easily.
– Thus, we can that the digital signature schemes are all based up on cryptography concepts and their effectiveness depends up on how well they have been implemented.
– Non repudiation is also provided by the digital signature which means that the signer cannot say that it was not him/ her who signed the message and their key is kept secret.
– There are various schemes for non – repudiation and some of them provide a time stamp facility to keep the signature valid even if the key get exposed.

Digital signatures might be anything such as:

  • Bit string
  • Contracts
  • Electronic mail
  • Some message sent via a cryptographic protocol etc.

Algorithms Constituting Digital Signature Scheme

Three algorithms together constitute the digital signature scheme:
1. Key generation algorithm: This algorithm is responsible for the selection of a private key from uniform random set of all private keys possible. The private key is given as the output along with a corresponding public key.
2. Signing algorithm: This algorithm is responsible for producing a digital signature using the message and the private key obtained by the first algorithm.
3. Signature verifying algorithm: This algorithm decides whether to accept or reject the claim to authenticity by a message provided a message, signature and the public key.

– In digital signature concept, two properties are very much important.
– Firstly, the authenticity of a message should be checked using the corresponding public key by the signature generated from a private key and message.
– Secondly, the generation of a valid signature should be in-feasible in terms of computation with the help of only private key.
– For the creation of RSA signature keys, a RSA key pair is required consisting a modulus N which is the result of multiplication of 2 primes.
– However, the security of this scheme is not much highly rated.
– For prevention of attacks, firstly a cryptographic hash function has to be applied to the message and then the RSA algorithm must be applied to the result.
– This approach is known to be secure in a model called as the random oracle model.
– A large number of earlier signature schemes were of same type i.e., they made use of the same traditional trap door permutation scheme (for example, RSA function).

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