Secret key

Using the secret key, one reconstructs the binary string M, and the graph G with all the extra edges added as in the embedding process. 

Take an image of size MxM Consider the image in DCT domain, where the Discrete Cosine Transform has been done using block size N/N. There is a secret key K and a secret watermarking signal w. The watermarking signal w = [nq,..., wt is t = bits binary pattern. 

Consider the case each DCT block where a bit is inserted. The key K is used as a seed of pseudo random number generator to get random index values from [Z, Z2], 1index values are matched with orders of the JPEG-like zigzag pattern in the DCT block. Now two index sets To and h, each containing 2n elements, are generated using the secret key Ki as follows ... 

This server maintains a database of secret keys for each entity, authenticates the identity of an entity that wishes to access network resources, and generates session keys when two entities wish to communicate securely. 

Encryption The process of converting information into a code or cipher. A secret key, or password, is required to decrypt (decode) the information, which would otherwise be unreadable. 

G - generator of synchronization sequences K - secret key for block cipher ... 

All containers are registered with a unique ID within the platform, which is kept by Platform Manager and is associated with shared secret key kID. The ID could be randomly generated or constructed based on, for example, the combination of device serial number and owner s identification number. 

V. After arrival agent requests the container to decrypt the carried random value with container s secret key N = DJN), then agent computes K = h(h(KJ N ), if hashed result h(K ) is equal to carried h(K) agent uses this as decryption key. 

There is only one secret key needed per mobile terminal (or per container) that is distributed manually upon service purchase. This secret key is stored in the container and is shared with the Platform Manager. It is used for secure and authenticated communication between the container and the Platform Manager. 

The random value N decrypted with target container s secret key KB equals initial random value N. 

The hash value of target container s secret key h(KB) equals the hash value returned by the Platform Manager. 

After arrival the agent requests the container to decrypt the carried random value with container s secret key N = DKJN). 

The carried content is decrypted if and only if values decrypted with container s secret key are equal to the values used for creation of the session encryption key, and if the current time is not later than the expiration date (i.e., target time). 

Hence, in classical cryptographic schemes, each pair or group of mutually trusting participants has a common secret key, and all the otiier information is public the schemes are therefore automatically symmetric. 

However, in the same article it was proved that any secrecy scheme that is provably secure in this sense is equivalent to one-time pads (see Section 1.5) or even less efficient. Thus, for a while, there was no further research in this field. Besides, for most applications, one-time pads were regarded as too inefficient, because the length of the secret key, which has to be exchanged beforehand, must be at least equal to the overall length of the messages that might be sent later. Hence one continued to use other schemes in practice. 

Such a scheme is intended to be used as follows Everybody who may want to sign messages generates such a key pair. She keeps the signing key secret and publishes the test key. (For simplicity, signers will always be assumed to be female and recipients male, corresponding to the names used in the figures.) Alternatively, the two keys are therefore called secret key (or private key) and public key, respectively. 

The main security requirement on such a digital signature scheme is, roughly speaking, that one cannot forge signatures although one knows the public key. A necessary (but not sufficient) condition for this is that one cannot compute the secret key from the public key. 

The same idea with key pairs was first introduced for secrecy schemes in [DiHe76] In this case, the first, more powerful, key is needed to decrypt messages, whereas with the second key, one can only encrypt. As before, the second key is published. Thus everybody can encrypt messages for the owner of a key pair and only the owner can decrypt them with the secret key. These schemes are called asymmetric secrecy schemes. ... 

With all symmetric schemes, each pair of participants who want to communicate securely must have exchanged its own secret key. Thus they must have met privately before, at least if one takes a strict point of view. With asymmetric schemes, in contrast, only one public key per participant needs to be distributed. 

In this work, as in all publications in theory, it is assumed that participants generate their own secret keys, so that the keys deserve the attribute secret . This procedure is also strongly recommended for practical applications. 

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