A digital signature is an electronic signature that can authenticate the identity of the sender of a message and ensure that the message has not been altered. Digital signatures are easily transportable, cannot be imitated, and are automatically time-stamped. A digital signature can be used with any message, whether encrypted or not, to verify the sender's identity and that the message was not changed. Digital certificates contain the digital signature of the certificate authority to verify that the certificate is authentic.

1. DIGITAL SIGNATURE RITU M-COM(E-COM)1ST YEAR

2. MEANING A digital signature is an electronic signature that can be used to authenticate the identity of the sender of a message or the signer of a document, and possibly to ensure that the original content of the message or document that has been sent is unchanged. Digital signatures are easily transportable, cannot be imitated by someone else, and can be automatically time-stamped. The ability to ensure that the original signed message arrived means that the sender cannot easily repudiate it later.

3. A digital signature can be used with any kind of message, whether it is encrypted or not, simply so that the receiver can be sure of the sender's identity and that the message arrived intact. A digital certificate contains the digital signature of the certificate-issuing authority so that anyone can verify that the certificate is real.

4. HOW IT WORKS

6. To secure information transmissionCipher text , text that has been encrypted and thus cannot be read by anyone beside the sender and the receiver. A key (or cipher )is any method for transforming plain text to cipher text.

7. Encryption has been practiced since the earlier forms or writing and commercial transactions. Commercial records were encrypted using substitution and transposition ciphers. Substitution cipher ,every occurrence of given letter is replaced systematically by another letter. If we used the cipher “letter plus two”-meaning replace every letter in a word with a new letter two places forward –then the word “ hello” in plain text would be transformed into the following cipher text: “JGNNQ” .

9. Spell the first word with every other letter beginning with the first letter,and then spell the second word with every other remaining letters. In this cipher “hello” would be written as “HLO EL”.

10. SYMMETRIC KEY ENCRYPTION In order to decipher these messages ,the receiver would have to know the secret cipher that was used to encrypt the plain text. This is called symmetric key encryption or secret key encryption. In symmetric key encryption ,both the sender and the receiver have the same key to encrypt and decrypt the message . They have send it over some communication media or exchange the key in person

11. Modern encryption system are digital .The cipher or key used to transform plain text into cipher text are digital strings. Computer store text or other data as binary strings composed of 0s and 1s. The most widely used symmetric key encryption on the internet today is the data encryption standards (DES) developed by the National Security agency and IBM .