This document discusses substitution and transposition encryption techniques. Substitution techniques replace plaintext characters with other characters, numbers, or symbols, changing character identity but not position. Transposition techniques rearrange the character positions in the plaintext, changing character position but not identity. Examples of substitution techniques include the Caesar cipher, monoalphabetic ciphers, Playfair cipher, and Vigenère cipher. Transposition techniques examples are the rail fence cipher and row transposition cipher.