Question

Nowadays many business transactions occur digitally using the Internet. Businesses must obtain the same level of assurance about the enforceability of a digital transaction that a signed document provides for a paper-based transaction. Digital signature is used to do accomplish this by using hashing and asymmetric encryption. Please use a diagram to explain the mechanism of asymmetric encryption through the use of public key and private key. Also, in Digital Signature, the private is used to encrypt the documents. Please explain why.

Answer 1

Answer

Asymmetric cryptography, also known as public key cryptography, uses public and private keys to encrypt and decrypt data. The keys are simply large numbers that have been paired together but are not identical (asymmetric). One key in the pair can be shared with everyone; it is called the public key. The other key in the pair is kept secret; it is called the private key. Either of the keys can be used to encrypt a message; the opposite key from the one used to encrypt the message is used for decryption.

Asymmetric encryption

Asymmetric encryption is quite the opposite to the symmetric encryption as it uses not one key but a pair of keys: a private one and a public one. One might ask:

Why do you need two keys?

You use one to encrypt your data, which is called public key, and the other to decrypt the encrypted message, which is called the private key.

When you encrypt your message using, let’s say, your granny’s public key, that same message can only be decrypted using her private key.

Private keys

Your private key, as the name states, is yours and it must be kept private, as it’s the only key that can decrypt any messaged that was encrypted with your public key.

Public keys

Public keys as, yet again, the name states, are public and thus no security is required because of it should publicly available and can be passed over the internet. The public key is used to encrypt a message that can only be decrypted using, as I written above, its private counterpart

PLAIN TEXT --> PUBLIC KEY --> CIPHER TEXT --> PRIVATE KEY --> PLAIN TEXT

Digital Signatures and Asymmetric Cryptography

Digital signatures are based on asymmetric cryptography and can provide assurances of evidence to origin, identity and status of an electronic document, transaction or message, as well as acknowledging informed consent by the signer. To create a digital signature, signing software (such as an email program) creates a one-way hash of the electronic data to be signed. The user's private key is then used to encrypt the hash, returning a value that is unique to the hashed data. The encrypted hash, along with other information such as the hashing algorithm, forms the digital signature.

Any change in the data, even to a single bit, results in a different hash value. This attribute enables others to validate the integrity of the data by using the signer's public key to decrypt the hash. If the decrypted hash matches a second computed hash of the same data, it proves that the data hasn't changed since it was signed. If the two hashes don't match, the data has either been tampered with in some way (indicating a failure of integrity) or the signature was created with a private key that doesn't correspond to the public key presented by the signer (indicating a failure of authentication).