GB/T 17964-2008 English PDF (GBT17964-2008)

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GB/T 17964-2008: Information technology -- Security techniques -- Modes of operation for a block cipher
GB/T 17964-2008
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 35.040
L 80
Replacing GB/T 17964-2000
Information technology - Security techniques -
Modes of operation for a block cipher
ISSUED ON: JUNE 26, 2008
IMPLEMENTED ON: NOVEMBER 01, 2008
Issued by: General Administration of Quality Supervision, Inspection and
Quarantine;
Standardization Administration of the People's Republic of
China.
Table of Contents
Foreword ... 4 
Introduction ... 5 
1 Scope ... 6 
2 Normative references ... 6 
3 Terms and definitions ... 6 
3.1 Terms ... 6 
3.2 Definitions ... 8 
4 Abbreviations and symbols ... 10 
5 Electronic codebook (ECB) operation mode ... 10 
5.1 Definition of variable ... 10 
5.2 Description of ECB encryption ... 10 
5.3 Description of ECB decryption ... 10 
6 Cipher block chaining (CBC) operation mode ... 11 
6.1 Definition of variable ... 11 
6.2 Description of CBC encryption ... 11 
6.3 Description of CBC decryption ... 12 
7 Cipher feedback (CFB) operation mode ... 13 
7.1 Definition of parameter ... 13 
7.2 Definition of variable ... 13 
7.3 Description of CFB encryption ... 13 
7.4 Description of CFB decryption ... 15 
7.5 Suggestion... 16 
8 Output feedback (OFB) operation mode ... 16 
8.1 Definition of parameter ... 16 
8.2 Definition of variable ... 17 
8.3 Description of OFB encryption ... 17 
8.4 Description of OFB decryption ... 18 
9 Counter (CTR) operation mode ... 19 
9.1 Definition of variable ... 19 
9.2 Description of CTR encryption ... 20 
9.3 Description of CTR decryption ... 21 
10 Block chaining (BC) operation mode ... 21 
10.1 Definition of variable ... 21 
10.2 Description of BC encryption ... 22 
10.3 Description of BC decryption ... 23 
11 Output feedback with a nonlinear function (OFBNLF) operation mode ... 23 
11.1 Definition of variable ... 23 
11.2 Description of OFBNLF encryption ... 24 
11.3 Description of OFBNLF decryption ... 24 
Annex A (normative) Nature of operation mode ... 26 
A.1 Nature of electronic codebook (ECB) operation mode ... 26 
A.2 Nature of cipher block chaining (CBC) operation mode ... 27 
A.3 Nature of cipher feedback (CFB) operation mode ... 29 
A.4 Nature of output feedback (OFB) operation mode ... 30 
A.5 Nature of counter (CTR) operation mode ... 31 
A.6 Block chaining (BC) operation mode ... 32 
A.7 Nature of output feedback with a nonlinear function (OFBNLF) operation mode ... 33 
Annex B (informative) Example of operation mode ... 35 
B.1 Overview ... 35 
B.2 ECB mode ... 35 
B.3 CBC mode ... 35 
B.4 CFB mode ... 36 
B.5 OFB mode ... 36 
B.6 CTR mode ... 37 
Bibliography ... 39 
Information technology - Security techniques -
Modes of operation for a block cipher
1 Scope
This Standard specifies seven operation modes of block cipher algorithm, so
as to standardize the use of block cipher.
2 Normative references
The provisions in following documents become the provisions of this Standard
through reference in this Standard. For dated references, the subsequent
amendments (excluding corrigendum) or revisions do not apply to this Standard,
however, parties who reach an agreement based on this Standard are
encouraged to study if the latest versions of these documents are applicable.
For undated references, the latest edition of the referenced document applies.
GB/T 1988-1998, Information technology - 7-bit Coded character set for
information interchange (eqv ISO/IEC 646:1991)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1 Terms
3.1.1 block chaining (BC) operation mode
an operation mode of block cipher algorithm; the current plaintext block is
different from the exclusive OR values of all previous ciphertext blocks or
operated then encrypted to obtain the current ciphertext block
3.1.2 block cipher
also known as block cipher algorithm; it is a symmetric cryptographic algorithm;
it divides plaintext into fixed-length blocks for encryption
3.1.3 block cipher operation mode
a use mode of block cipher algorithm, mainly including electronic codebook
(ECB) operation mode, cipher block chaining (CBC) operation mode, cipher
starting data that is brought for data transformation so as to increase security
or synchronize cipher devices during cryptographic transformation
3.1.14 key
key information or parameter that controls cryptographic transformation
3.1.15 output feedback with a nonlinear function (OFBNLF) operation
mode
an operation mode of block cipher algorithm; it is a variant of OFB and ECB; its
key varies with each block
3.1.16 output feedback (OFB) operation mode
an operation mode that block cipher algorithm is used to construct sequence
cipher; use the output of the current time of this algorithm as the input of the
next moment
3.1.17 plain text/clear text
data to be encrypted
3.2 Definitions
3.2.1 Encryption expression
In this Standard, the functional relationship specified by block cipher is recorded
as:
Where,
P is plaintext block;
C is ciphertext block;
K is key;
EK is encryption operation that uses key K.
3.2.2 Decryption expression
The corresponding decryption function is recorded as:
A special case of this function starts with the m-bit variable I(m) of all "1"s and
moves the k-bit variable F into it. The result is:
Where, the left-most m-k bit is "1".
4 Abbreviations and symbols
AES advanced encryption standard
BC block chaining
CBC cipher block chaining
CFB cipher feedback
CTR counter
DEA data encryption algorithm
ECB electronic codebook
IV initialization value
OFB output feedback
OFBNLF output feedback with a nonlinear function
5 Electronic codebook (ECB) operation mode
5.1 Definition of variable
a) Sequence consisting of q plaintext blocks P1, P2, ..., Pq. Each block is n
bits.
b) Key K.
c) Result sequence consisting of q ciphertext blocks C1, C2, ..., Cq. Each
block is n bits.
5.2 Description of ECB encryption
5.3 Description of ECB decryption
7 Cipher feedback (CFB) operation mode
7.1 Definition of parameter
Size of feedback buffer r (n≤r≤2n);
Size of feedback variable k (1≤k≤n);
Size of plaintext variable j (1≤j≤k).
NOTE: r-k can be less than n. Figure 2 shows special case of r-k >n.
7.2 Definition of variable
a) Input variable
1) Sequence consisting of q plaintext blocks P1, P2, ..., Pq. Each block is j
bits.
2) Key K.
3) Initialization value of r-bit IV.
b) Intermediate results
1) Sequence consisting of q key input blocks X1, X2, ..., Xq. Each block is
n bits.
2) Sequence consisting of q key output blocks Y1, Y2, ..., Yq. Each block
is n bits.
3) Sequence consisting of q variables Z1, Z2, ..., Zq. Each block is j bits.
4) Sequence consisting of q-1 feedback variables F1, F2, ..., Fq-1. Each
variable is k bits.
5) Sequence consisting of q-1 feedback buffer contents FB1, FB2, ..., FBq-
1. Each block is n bits.
c) Output variable
Sequence consisting of q ciphertext variables C1, C2, ..., Cq. Each block is
j bits.
7.3 Description of CFB encryption
Initialization value of feedback buffer FB is:
e) Generate feedback variable:
f) FB bit-shift operation:
For i=1, 2, …, q, repeat the above steps. The last cycle ends at step d). This
process is shown in the right ...