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AssigneeLucent Technologies Inc.
InventorsSarvar Patel, Zulfikar Amin Ramzan, Ganapathy Subramanian Sundaram
Estimating the term…
A hash function is applied to a prefix of a VIL input. The output is added to a suffix of the input. A block cipher is applied to results of the addition. An encryption function is performed on the prefix. The final output is the output of the block cipher and the encryption function. In a second encryption technique, a hash function is applied to an input, and the output of the hash function has first and second portions. A block cipher is applied to the second portion. The output of the block cipher is added to the first portion, and a second function is applied to the result of this first addition. The output of the second function is added to the second portion. An inverse hash function is then applied to the output of the first and second additions, creating an encrypted output.
A method of encrypting an input, comprising:
An apparatus for encrypting an input, comprising:
A method for decryption, comprising:
An apparatus, comprising:
A method for encryption, comprising:
An apparatus for encryption, comprising:
A method for decryption, comprising:
An apparatus for decryption, comprising:
Dependencies are inferred from the claim text.
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The encryption apparatus using shift registers or memories for block-wise or stream coding, e.g. DES systems or RC4; Hash functions;…
Block ciphers, i.e. encrypting groups of characters of a plain text message using fixed encryption transformation: modes of operation, e.g. cipher…
Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols: using hash chains, e.g.…
Additional information or applications relating to cryptographic mechanisms or cryptographic arrangements for secret or secure communication…
Term end not estimated
The present invention relates generally to cryptography, and more particularly, to constructions of variable input length cryptographic primitives for high efficiency and high security.
A cryptographic primitive that operates on an input of fixed size is called a Fixed Input Length (FIL) primitive. For example, all block ciphers, which are common FIL primitives, operate on messages of fixed size. Informally, a block cipher is a type of encryption algorithm that transforms a block of unencrypted text (commonly called “plaintext”) into a block of encrypted text (commonly called “ciphertext”). The plaintext and ciphertext have the same length when transformed through a block cipher. This transformation takes place under the action of a secret key. Decryption is performed by applying a reverse transformation to the ciphertext block using the same secret key. The length of a block is called the block size, and, for many block ciphers, the block size is 64 or 128 bits.
However, in practice, one is faced with the situation of applying a cryptographic primitive on data of varying lengths. This situation calls for the development of cryptographic primitives called Variable Input Length (VIL) primitives. One particular situation is the need for an encryption algorithm which deals with messages of varying sizes but at the same time preserves the property that the length of the ciphertext equals the length of the plaintext. This situation is very common in Internet applications, where traffic consists of “packets” of varying sizes. If a block cipher is being used for encryption, then the blocks that need to be encrypted could be of varying lengths.
FIG. 1 illustrates a block diagram of an exemplary system implementing cryptographic constructions in accordance with a preferred embodiment of the invention;
FIG. 2 illustrates a block diagram of a block cipher construction in accordance with a preferred embodiment of the invention;
FIG. 3 is a flowchart of a method of decrypting the output of the block cipher construction of FIG. 2;
The following detailed description is divided into several sections in order to facilitate an organized description of the embodiments of the present invention. In Section 1, an overview of the embodiments of the present invention is given. Section 2 contains a variety of definitions that are used in subsequent sections. Section 3 describes techniques for encrypting and decrypting data using Variable Input Length (VIL) PseudoRandom Permutations (PRP). To simplify understanding, these techniques are presented by showing how conventional techniques may be converted to techniques of the present invention. The VIL PRP encryption and decryption techniques of the present invention are described mathematically and in relation to FIGS. 2 and 3. Section 4 describes techniques for encrypting and decrypting VIL data using Strong-PRP. Basically, PRP is secure against plaintext attacks, while Strong-PRP is secure from both plaintext and ciphertext attacks. Again, these VIL Strong-PRP techniques are presented by showing how conventional techniques may be converted to the techniques of the present invention. Encryption and decryption techniques of the present invention are described mathematically and in relation to FIGS. 4 and 5.
1. Overview
Broadly, techniques of the present invention allow Variable Input Length (VIL) inputs to be encrypted. There are basically two classes of VIL techniques, “variable but fixed” and “variable in and variable out.” In the former, an input having one length is converted to an output having the same length. For instance, an input of 1024 bits is converted to an output having 1024 bits. In “variable in and variable out,” an input having one length is converted to an output having a different length. For example, an input of 1024 bits is converted to an output having 512 bits. The techniques of the present invention are “variable but fixed” VIL cryptographic techniques. The techniques of the present invention are variable because the size of the input is allowed to vary, as opposed to a fixed input length cryptographic technique where the input must be a particular size or perhaps an integer factor of the particular size. In other words, fixed input length cryptographic techniques can have an input of 1024 bits, for instance, or perhaps 2048 or 4086 bits, while the techniques of the present invention can be designed to operate on 517 bits or 1045, or some other suitable number of bits.