Encryption

Encryption is the process of transforming plain text or data into cipher text that cannot be read by anyone other than the sender and the receiver. The purpose of encryption is (a) to secure stored information and (b) to secure information transmission. Encryption can provide four of the six key dimensions of e-commerce security: message integrity, nonrepudiation, authentication, and confidentiality.

This transformation of plain text to cipher text is accomplished by using a key or cipher — any method for transforming plain text to cipher text. Encryption has been practiced since the earliest forms of writing and commercial transactions. Ancient Egyptian and Phoenician commercial records were encrypted using substitution and transposition ciphers.

In a substitution cipher, every occurrence of a given letter is replaced systematically by another letter. For instance, using the cipher 'letter plus two' (replace every letter with a new letter two places forward), the word 'Hello' becomes 'JGNNQ.' In a transposition cipher, the ordering of the letters in each word is changed in some systematic way. Leonardo Da Vinci recorded his shop notes in reverse order, making them readable only with a mirror.

Modern encryption systems are digital: the ciphers or keys used to transform plain text into cipher text are digital strings. The strength of modern security protection is measured in terms of the length of the binary key used to encrypt the data. Modern systems use keys with 56, 128, 256, or 512 binary digits. With 512-bit keys, there are 2^512 possibilities to check — it is estimated that all the computers in the world would need to work for 10 years to break such a key by brute force. The two main families of modern encryption are symmetric key cryptography and public key (asymmetric) cryptography, examined in the following topics.