1 The word cryptography comes from the Greek words kryptos meaning hidden and graphein meaning writing. Cryptography is the study of hidden writing, or the science of encrypting and decrypting text.

2 Nineteenth century scholars decrypted ancient Egyptian hieroglyphics when Napoleon's soldiers found the Rosetta Stone in 1799 near Rosetta, Egypt. Its inscription praising King Ptolemy V was in three ancient languages: Demotic, hieroglyphics, and Greek. The scholars who could read ancient Greek, decrypted the other languages by translating the Greek and comparing the three inscriptions.

3 In the twentieth century world of computer networks, messages are digitally encrypted on the sending side and decrypted on the receiving side using cryptographic services and algorithms. Algorithms are mathematical techniques or rules that apply a cryptographic service to a message. Cryptographic services include hashing a message, encrypting and decrypting a message, and signing or verifying the signature on a message. A message digest object uses a hashing algorithm to make a hash digest of the original message, key pairs use a key algorithm compatible with the hashing algorithm to encrypt and decrypt the message, and a signature object uses the key pairs to sign and verify the signature on a message.

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