Abstract
The concept of Identity Based Cryptography introduced the idea of using arbitrary strings such as e-mail addresses and IP Addresses to form public keys with the corresponding private keys being created by the Trusted Authority(TA) who is in possession of a system-wide master secret. Then a party, Alice who wants to send encrypted communication to Bob need only Bob's identifier and the system-wide public parameters. Thus the receiver is able to choose and manipulate the public key of the intended recipient which has a number of advantages. While IBC removes the problem of trust in the public key, it introduces trust in the TA. As the TA uses the system-wide master secret to compute private keys for users in the system, it can effectively recompute a private key for any arbitrary string without having to archive private keys. This greatly simplifies key management as the TA simply needs to protect its master secret.
TopBackground
The public key encryption is a cryptographic system that uses two keys -- a public key known to everyone and a private or secret key known only to the recipient of the message. When user Alice wants to send a secure message to user Bob, she uses Bob's public key to encrypt the message, Bob then uses his private key to decrypt it. An important element to the public key system is that the public and private keys are related in such a way that only the public key can be used to encrypt messages and only the corresponding private key can be used to decrypt them. Moreover, it is virtually impossible to deduce the private key if you know the public key. Users will exchange public keys; this transaction does not need to be done in a secure manner because the release of public keys does not threaten the security of any private information. After this swap, someone who wishes to send private information to another user will encrypt the data with the intended recipient’s public key and then pass along the encrypted message. The recipient, who will keep his or her private key secure under any circumstance, can use the private key to decrypt the encoded message.
Key Terms in this Chapter
Ciphertext: The term ciphertext refers to the output message from an encryption algorithm.
Pairing Based Cryptography: The cryptographic algorithms that use the Mathematics of pairings. The most commonly used pairings include Tate Pairing, Weil Pairing etc.
Identity: Refers to a string that is used to identify an individual. For example, an e-mail address.
Trusted Authority: The Trusted Authority is a third party trusted to distribute keys. In the Identity Based Encryption Schemes, the Trusted Authority provide secret keys.
Hash Algorithm: This produces a fixed size output given a message as input. This output can be used to verify message contents.
Signatures: Signing of a message by one’s private key. The hash of a message is encrypted with the private key.
Identity Based Cryptography: The algorithms that generate the public key using an id of the user. The private key should be obtained from a Trusted Authority.
Plaintext: The term plaintext refers to the input message to an encryption algorithm.
Authentication: refers to verifying the identity of a particular user.
Random Oracle Model: This model assumes the presence of oracle which returns answers to queries similar to Hash functions. It is suggested that the Oracle be implemented through Hash functions.
Public Key: The Public key is one of the keys used in public key encryption algorithms. This key is made available publicly.
Adversary: An attacker who may try to guess the secret key or the plaintext from a given ciphertext.
Private Key: The secret key in the public key encryption algorithms. This key is kept secret.