METHOD OF GENERATING MESSAGE AUTHENTICATION CODE USING STREAM CIPHER AND AUTHENTICATION/ENCRYPTION AND AUTHENTICATION/DECRYPTION METHODS USING STREAM CIPHER

• US 20080112561A1
• Filed: 11/12/2007
• Published: 05/15/2008
• Est. Priority Date: 11/13/2006
• Status: Active Grant

• Current Assignee: Nainfox Co., Ltd.
• Original Assignee: Electronics and Telecommunications Research Institute
• Inventors: LEE, Jung Keun, KIM, Woo Hwan
• Granted Patent: US 8,090,098 B2
• Time in Patent Office: Days
• US Class Current: 380/42
• CPC Class Codes: H04L 2209/125 Parallelization or pipelining, e.g. for accelerating processing of cryptographic operations
• CPC Class Codes: H04L 9/0643 Hash functions, e.g. MD5, SHA, HMAC or f9 MAC
• CPC Class Codes: H04L 9/0662 with particular pseudorandom sequence generator
• CPC Class Codes: H04L 9/3242 involving keyed hash functions, e.g. message authentication codes [MACs], CBC-MAC or HMAC
• CPC Class Codes: H04L 9/50 using hash chains, e.g. blockchains or hash trees

Abstract

Provided are a method of generating a Message Authentication Code (MAC) using a stream cipher, and authentication/encryption and authentication/decryption methods using a stream cipher.

According to the methods, authentication/encryption is performed using a MAC generated using a stream cipher as an initialization vector of the stream cipher. Therefore, it is unnecessary to use a random number generation algorithm to generate the initialization vector, and thus implementation efficiency can be improved.

In addition, upon generation of a MAC, a plurality of key stream generators perform computation for a plurality of message blocks, respectively. Therefore, the message blocks are computed in parallel at a time, and thus computation efficiency is excellent.

Claims

1. A method of generating a Message Authentication Code (MAC) using a stream cipher, comprising the steps of:

(a) dividing an input message M into k n-bit message blocks;

(b) encrypting the respective divided input message blocks using a result obtained by exclusive-ORing (XORing) a secret key K_MAC for MAC generation with a number among the number k of the message blocks divided in step (a), as a key, and calculating respective intermediate values;

(c) XORing the respective intermediate values resulting from step (b); and

(d) encrypting, at a key stream generator, the result of step (c) using the secret key K_MAC for MAC generation and generating a MAC.

2. The method of claim 1, wherein in step (b), the respective intermediate values h_i are calculated by the following formula:

h_i=E_n(K_MAC⊕

i,m_i),

wherein the k n-bit message blocks obtained by dividing the input message M are denoted by m₁, m₂, . . . , m_k, one of the message blocks is denoted by m_i, and E_n(K, m_i) denotes an encryption algorithm performed for the message blocks m_i using K as a key by the key stream generator.

3. The method of claim 2, wherein in step (c), the respective intermediate values are XORed by the following formula:

h=⊕

_i=1^kh_i,

wherein h denotes a value obtained by XORing the respective intermediate values.

4. The method of claim 3, wherein in step (d), the MAC is expressed by the following formula:

MAC(K_MAC,M)=E_n(K_MAC,h),

wherein MAC(K_MAC, M) denotes the MAC.

5. The method of claims 1, wherein in step (a), when lengths of the respective message blocks m₁ to m_k are not a multiple of n, the lengths are made to be a multiple of n.

6. The method of claim 5, wherein the lengths of the respective message blocks m₁, . . . , m_k are made to be a multiple of n by adding 100 . . . 0 to the respective message blocks m₁ to m_k.

7. The method of claims 1, wherein in step (b), the respective intermediate values are calculated in parallel.

8. An authentication/encryption method using a stream cipher, comprising the steps of:

(a) inputting a plaintext M and a secret key K_MAC for Message Authentication Code (MAC) generation and generating a MAC MAC(K_MAC, M) for the plaintext M;

(b) setting the MAC MAC(K_MAC, M) generated in step (a) as a stream cipher initialization vector IV;

(c) generating an n-bit key stream using the MAC MAC(K_MAC, M), which is the stream cipher initialization vector IV, and a secret key K_ENC for message encryption;

(d) exclusive-ORing (XORing) the generated key stream with the plaintext M to generate a ciphertext C; and

(e) outputting the ciphertext C.

9. An authentication/decryption method using a stream cipher, comprising the steps of:

(a) generating a key stream using a stream cipher initialization vector IV and a secret key K_ENC for message encryption; and

(b) exclusive-ORing (XORing) the key stream with a ciphertext C to generate a plaintext M.

10. The method of claim 9, further comprising the steps of:

(c) generating a Message Authentication Code (MAC) MAC(K_MAC, M) for the plaintext M; and

(d) when the stream cipher initialization vector IV is the same as the MAC MAC(K_MAC, M), determining the ciphertext C as a valid ciphertext (IV, C) and outputting the plaintext M for the valid ciphertext (IV, C).

11. The method of claim 10, wherein in step (d), when the stream cipher initialization vector IV is not the same as the MAC MAC(K_MAC, M), an error message is output.

12. The method of claim 10, wherein in step (c), the MAC MAC(K_MAC, M) for the plaintext M is generated from the plaintext M and a secret key K_MAC for MAC generation.