digital signature

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digital signature

[′dij·əd·əl ′sig·nə·chər]
(communications)
A set of alphabetic or numeric characters used to authenticate a cryptographic message by ensuring that the sender cannot later disavow the message, the receiver cannot forge the message or signature, and the receiver can prove to others that the contents of the message are genuine and originated with the sender.

digital signature

(cryptography)
Extra data appended to a message which identifies and authenticates the sender and message data using public-key encryption.

The sender uses a one-way hash function to generate a hash-code of about 32 bits from the message data. He then encrypts the hash-code with his private key. The receiver recomputes the hash-code from the data and decrypts the received hash with the sender's public key. If the two hash-codes are equal, the receiver can be sure that data has not been corrupted and that it came from the given sender.

digital signature

A digital signature is the electronic equivalent of a person's physical signature. It is also a guarantee that information has not been modified, as if it were protected by a tamper-proof seal that is broken if the contents were altered.

Signed Certificates
Digitally signed certificates verify the identity of an organization or individual. Signed certificates are widely used to authenticate a website and establish an encrypted connection for credit cards and confidential data (see digital certificate, SSL and TLS).

Signed Files
Files of any kind can be signed; however, a common application is "code signing," which verifies the integrity of executables downloaded from the Internet. Code signing also uses certificates (see code signing and digital certificate).

An Encrypted Digest
A digital signature is actually an encrypted digest of the data being signed. The digest is computed from the contents of the file by a one-way hash function (see below) and then encrypted with the private key of the signer's public/private key pair. To prove that the file was not tampered with, the recipient uses the public key of the signer to decrypt the signature back into the original digest, recomputes a new digest from the transmitted file and compares the two to see if they match. If they do, the file has not been altered in transit by an attacker. See RSA, MD5, SHA, public key cryptography and electronic signature.


An Encrypted Digest
A digital signature is an encrypted digest of a file. The digest was created with a one-way hash function from the file's contents.







With and Without Privacy


The following two diagrams show how digital signatures are used for data integrity in both non-private and private transmissions.


Message Integrity Without Privacy
The woman makes her message tamper proof by encrypting the digest into a "digital signature," which accompanies the message. At the receiving side, the man uses her public key to verify the signature. However, the message text is sent "in the clear" and could be read by an eavesdropper.








Message Integrity With Privacy
In this example, the message is both signed and transmitted in secret. The woman signs the message first and then entirely encrypts it before sending. The man decrypts the message first and then verifies the signature.
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I don't want to talk too much about this but all the clubs around the world know they (Heinze's representatives) have a signed document, so they know the situation, and I don't see what the problem is," said the Liverpool manager.
Many do not realize that when they send an e-mail it is considered a signed document.
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Prime Minister Habib Essid described work of the joint committee as "positive," saying the signed documents, which cover most of the areas of bilateral co-operation, will help "hoist bilateral relations to higher levels.
Electronically signed documents are then securely managed and stored in a repository, known as an electronic vault.
Always have an independent legal representative look over all documents before you sign them, keep copies of all signed documents and make sure you have read every document relating to your loan or transaction.
Lyon said he had signed documents when and where he was told to do so, without reading them.
A central government official on Tuesday signed documents to continue the forcible lease of sites in Okinawa Prefecture to the U.
Contract notice: Procurement of a tr-esor middleware for evidence value of cryptographically signed documents according to bsi tr-esor (tr 03125) and their care.
The SEC is alleging that a nonexecutive employee at Pepsi-Cola and another at Frito-Lay signed documents in early 2001 prepared by what is now called Kmart Holding Corp.
The five Americans declined to talk to reporters as they left the immigration office in Puerto Vallarta, where they signed documents pledging not to leave the country.
The SAFE standard provides a secure, legally enforceable, and regulatory compliant way to provide identity verification, non repudiation, and content integrity for electronically signed documents.