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A cipher is a method of hiding words or text with encryption by replacing original letters with other letters, numbers and symbols through substitution or transposition. A combination of substitution and transposition is also often employed.Cipher also refers to the encrypted text, cryptography system or encryption key for the original text. Encrypted text is also known as ciphertext. Plaintext is the original, unencrypted text.
A cipher enables private communication and is often used in email, so that if an encrypted message is intercepted by an unauthorized user, the message cannot be read.
A block cipher encrypts plaintext with a key and algorithm, which affects a complete block of data containing several bits. This may mean 64 bits of encryption for every one bit of data. A stream cipher encrypts plaintext with a key and algorithm applied to every binary digit (ones and zeros) for every bit in the data stream. Today, this type of cipher is not as common as the block cipher.
A number of other cipher types exist. Two typical examples are: