A digital signature can be used to make sure that an electronic document like text file, email, spreadsheet, etc is authentic. A digital signature helps to know the creator of the document and also to ensure that the document has not been altered in any way.
Encrypted to ensure authenticity: Digital signatures are based on certain types of encryption system to ensure authentication. To use encryption or digital certificate, a digital id known as digital certificate is required. It can be used for two purposes. Firstly, it can be used to encrypt files or email encryption so that the document can only be read by the intended person. Secondly, it can be used to place digital signature or digitally sign a document to ensure that the document arrived in the exact state and no alteration has been made.
Used with a private and Public Key: A digital certificate or id consists of a private and public key. The public key is shared with all; however the private key is kept private. The keys are nothing but text documents with random letters and numbers. But if the document is run through an algorithm along with the public key, it will produce an encrypted email or document. Once a document is encrypted, the use of public key will not decrypt the document and thus people with public key will not be able to read the document. The decryption of the document is possible only with the help of private key along run through some algorithm that will produce the original document.
Hash Values to check if any alteration is done: A combination of public and private key is used public key encryption. The private key is known only to one computer whereas the public key is provided to any other computer that wants to communicate with it securely. The key is based on a hash value computed from a base input number by using some sort of hashing algorithm. So when messages are signed with digital signatures, the hash value makes sure that no alteration has been done with the document. Encryption of the hash value by using the private allows verifying no alteration has been done with the hash value using the public key. These processes are generally handled by the software and warning messages are produced in case the hash value is different.
Verifying is facilitated by Digital Signature: Signing a document with digital signature ensures that the document is actually sent by the concerned person, the document was not modified and it cannot be read by anybody. It is quite easy for people to verify a digital signature without the need to get a digital certificate or id for themselves.
Uses checksum for ensuring data is correct: Checksum is probably one of the oldest methods to ensure that the data is correct. Back in the days when computers were recently introduced, computers used to send an eight bit byte with the last bit as a checksum. The last bit was used to know if there were odd or even number of one’s present in the data. If the receiving computer agreed with the checksum value then the data was successfully transferred.
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