One fascinating way of ensuring security of electronic data is to embed it within an image and to transmit the image to desired recipient. An image being a collection of pixels and even a single pixel being a collection of binary digits, replacement of some less significant binary digits by binary digits corresponding to aforesaid data does not practically make a change to that image, when viewed in naked eyes. Therefore, even the existence of secret data within that image is hard to realize. The formulation of effective strategies to implement this concept, technically termed as Steganography, has been a burning area of research for last several years. Over the years, encryption has been a means of protecting electronic data. Prior to its transmission, data is encoded using an encryption algorithm. Apart from the original data, a value, termed as key, is fed into the encryption program to encode the data to generate the ready-to-be-transmitted encrypted data. In receiving end, the encrypted data, along with a key, is fed into the decryption program to decode the encrypted data. Thus for a communication of data over a transmission channel, both the ends of the channel can be equipped with encryption devices, one for performing encryption and the other for doing the reverse. Incidentally, keys used in both ends of transmission channel may be identical or different. In former case, termed as private-key encryption policy, the key-sharing requires a lot of care to maintain the privacy. The headache of key-sharing is avoided in public-key encryption policy by using a pair of keys, the public key of receiver during encryption and the private key of receiver during decryption. Authentication is closely associated with security. One can send an authenticated or digitally signed electronic message by encrypting it with his own private key, which, in receiving end, can only be decrypted through the corresponding public-key. Developing public-key encryption policy with proven efficiency is one striking challenge for researchers. However, even a private-key policy with a reasonably large key-space is arguably compatible with a public-key policy. As per an appealing observation, even a fast processor with capability of decrypting 1000000 decryptions in 1 µs requires around 5000000000000000000 years to successfully break a 128-bit private-key used during a common implementation of Rijndael, a proposed private-key policy selected by NIST (US-based National Institute of Standards and Technology) as an AES (Advanced Encryption Standard) algorithm. If an image with encrypted message embedded into it is digitally signed, it becomes fairly non-vulnerable against possible attacks.
(From the draft to write invited article for a technical newsletter)
