It was the early 1990's, when I was in my high school. Lamination as a technology and as a industry was growing and touching our everyday lives - in the form of laminated identity card, laminated report card, laminated photographs etc... It protected the cards and photographs from being smudged or stained.
We were then quite surprised by the 'neat and clean' work done, through lamination, and it became so entrenched in our conversations, a new phrase called "Laminated Truth" was created - to mean absolute truth! and to convey that the information or message heard (invariably over heard) by that person has not been altered or modified in any way. Determining the truthfulness of this "laminated truth" is entirely a different matter altogether ...
Coming back to today's digital world, where "cut & paste" is the norm, and documents could easily be forged, how do you achieve this "laminated truth"? - The answer is Cryptography. A mathematical one-way function called Cryptographic Hash Function produces a fixed-size bit string for the input message. The beauty of this function is that any alteration in the input message, even as insignificant as punctuation, will produce a different output bit string. For instance "Its mine" and "Its mine." will produce different bit strings, as the second message contains a period at the end.
The fixed-size output bit string produced by the Cryptographic Hash Function is called as "Message Digest", which form the basis for a "Digital Signature". The digital signature is nothing but the encryption of the "Message Digest" by using a key that is personal (private key) to the author or signer of the message. This encrypted digital signature could then be decrypted only by using the one and the only another key that has a mathematical pairing with the key used for encryption, and which is generally announced publicly (public key) by the author or signer.
Therefore the signer has a pair of keys with him or her - One of them is announced publicly - called public key, another is kept secretly - called private key. A message encrypted using public key could be decrypted only by using the private key, and a message encrypted by using private key could only be decrypted using the public key. The digital signature provides a reliable mechanism for anybody to determine whether a message is indeed a laminated truth!
