A steganographic substitution technique using APPM for encrypted pixels

Pixel pair matching (PPM) is a method for hiding secret data inside a cover pixel using two pixel pair co-ordinates. One pixel pair is used as reference co-ordinate and the other is used as the reference co-ordinate. It is one form of substitution methods. Adaptive pixel pair matching (APPM) is the one variant of the PPM where the former differs from the latter in the extraction function it utilizes. APPM achieves good embedding capacity. Encrypting the cover pixel before data embedding enhances the system security. Thus, this paper aims in embedding secret information into an encrypted cover image. Combined form of Cryptography and Steganography is the added feature of this paper. Stream Ciphered cover image is subjected to the APPM data embedding. The key that is used at the transmitter for encryption is used at the receiver for decryption. The decrypted image is then extracted to obtain the hidden information.