# US 9,002,011 B2 · Method for generating consistent cryptographic key based on wireless channel features

> Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt

- Number: US 9,002,011 B2
- Document ID: US9002011B2
- Status: Granted
- Kind: B2
- Application number: 14/130,308
- Filed: 2011-06-30
- Published: 2014-05-22
- Granted: 2015-04-07
- Earliest claimed: 2011-06-30
- Assignees: Beijing University of Posts and Telecommunications
- Applicants: Yuexing Peng; Kan Zheng; Guangwei Li
- Inventors: Yuexing Peng; Kan Zheng; Guangwei Li
- Web page: https://patentgrep.com/patent/US9002011B2

## CPC

- H04W 74/00: Wireless channel access
- H04L 9/0861: {Generation of secret information including derivation or calculation of cryptographic keys or passwords}
- H04L 9/0875: {based on channel impulse response [CIR]}
- H04W: WIRELESS COMMUNICATION NETWORKS (broadcast communication H04H; communication systems using wireless links for non-selective communication, e.g. wireless extensions H04M1/72)
- H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M)

## Abstract

The present invention discloses a method for generating a consistent cryptographic key based on wireless channel features. First of all, channel estimated values ĥa, ĥb and channel estimate mean square error MSE are obtained through channel estimate, and then quantized channel eigenvectors {tilde over (h)}a and {tilde over (h)}b are obtained through quantization coding; next, inconsistency between {tilde over (h)}b and {tilde over (h)}a is equivalent to obtaining {tilde over (h)}b at end B through virtual channel noise adding the channel eigenvector {tilde over (h)}a sent by end A, and Signal-to-Noise ratio SNR Γ of the virtual channel is determined; a proper coding mode ENC is determined according to the virtual channel SNR Γ; both communication parties perform corresponding coding and decoding according to ENC and thereby obtain an estimated value {tilde over (ĥ)}a of {tilde over (h)}a; finally, a cryptographic key generating function is applied to {tilde over (h)}a and {tilde over (ĥ)}a, whereby a cryptographic key Kc is obtained. The present invention increases the validity of consistent dynamic cryptographic key generating and achieves information security and privacy at the physical layer.

## Claims

### Claim 1

A method for generating a consistent cryptographic key based on wireless channel features, characterized by comprising:
(1) according to a preset channel estimate method CE, both communication ends A and B respectively performing channel estimate to a current channel, obtaining channel estimated values ĥa, ĥb and channel estimate mean square error MSE, and defining MSE=f1(CE,γ) according to current channel Signal-to-Noise ratio (SNR) γ, where f1 represents a relational expression between the current channel Signal-to-Noise ratio γ and the channel estimate mean square error MSE when using the channel estimate method CE;
(2) according to a preset quantization mode and quantization step, performing quantization encoding to the obtained channel estimated values ĥa, and ĥb respectively, thereby obtaining quantized channel eigenvectors {tilde over (h)}a and {tilde over (h)}b;
(3) letting inconsistency between the channel eigenvector {tilde over (h)}b of end B and the channel eigenvector {tilde over (h)}a of end A, i.e. {tilde over (h)}b={tilde over (h)}a+e be equivalent to obtaining {tilde over (h)}b at end B through virtual channel noise adding the channel eigenvector {tilde over (h)}a sent by end A, where SNR of the virtual channel is
Γ
=

h
~
a

2
E
⁡
(

e

2
)
=
1
4
⁡
[
f
1
⁡
(
CE
,
γ
)
+
MSE
Q
]
,
wherein e represents total quantization error of channel estimate results of ends A and B, and MSEQ represents quantization mean square error that is decided by the quantization step;
(4) according to the virtual channel SNR Γ, determining a proper encoding mode ENC such that its error correction performance matches expected bit error rate BER, i.e. ENC=f2−1(BER,Γ), wherein f2 represents a relational expression between the virtual channel SNR Γ and the bit error rate BER in a coding mode ENC, and f2−1 represents the inverse operation of f2;
(5) end A coding the channel eigenvector {tilde over (h)}a using the determined coding mode ENC and thereby obtaining a check sequence Pa; after receiving Pa, end B inputting Pa together with the channel eigenvector {tilde over (h)}b in the end into a decoder corresponding to ENC for decoding, and thereby obtaining an estimated value {tilde over (ĥ)}a of {tilde over (h)}a; and
(6) end A and end B applying a cryptographic key generating function on {tilde over (h)}a, and {tilde over (ĥ)}a respectively to obtain a cryptographic key Kc, wherein Kc=f3 ({tilde over (ĥ)}a,N) wherein N is the length of the cryptographic key and f3 is the cryptographic key generating function.

### Claim 2 (depends on 1)

The method according to claim 1, characterized by further comprising:
(7) performing privacy amplification and cryptographic key confirmation to the obtained cryptographic key Kc.

### Claim 3 (depends on 1)

The method according to claim 1, characterized in that the expression f1 is obtained according to theoretical analysis or numerical simulation.

### Claim 4 (depends on 1)

The method according to claim 1, characterized in that the expression f2 is obtained according to theoretical analysis or numerical simulation.

### Claim 5 (depends on 1)

The method according to claim 1, characterized in that the expected bit error rate BER is determined according to the virtual channel SNR Γ and channel eigenvector length L, wherein L is determined by cryptographic key length and quantization mode.

### Claim 6 (depends on 1)

The method according to claim 1, characterized in that the error correction performance of the coding mode ENC is one to two orders of magnitude higher than the expected bit error rate BER.

### Claim 7

A method for determining a coding mode matching current channel features, characterized by comprising:
(1) according to a preset channel estimate method CE, both communication ends A and B respectively performing channel estimate to a current channel, obtaining channel estimated values ĥa, ĥb and channel estimate mean square error MSE, and defining MSE=f1(CE,γ) according to current channel Signal-to-Noise ratio (SNR) γ, where f1 represents a relational expression between the current channel Signal-to-Noise ratio γ and the channel estimate mean square error MSE when using the channel estimate method CE;
(2) according to a preset quantization mode and quantization step, performing quantization encoding to the obtained channel estimated values ĥa and ĥb respectively, thereby obtaining quantized channel eigenvectors {tilde over (h)}a and {tilde over (h)}b;
(3) letting inconsistency between the channel eigenvector {tilde over (h)}b of end B and the channel eigenvector {tilde over (h)}a of end A, i.e. {tilde over (h)}b={tilde over (h)}a+e be equivalent to obtaining {tilde over (h)}b at end B through virtual channel noise adding the channel eigenvector {tilde over (h)}a sent by end A, where SNR of the virtual channel is
Γ
=

h
~
a

2
E
⁡
(

e

2
)
=
1
4
⁡
[
f
1
⁡
(
CE
,
γ
)
+
MSE
Q
]
,
wherein e represents total quantization error of channel estimate results of ends A and B, and MSEQ represents quantization mean square error that is decided by the quantization step; and
(4) according to the virtual channel SNR Γ, determining a proper encoding mode ENC such that its error correction performance matches expected bit error rate BER, i.e. ENC=f2−1(BER,Γ), wherein f2 represents a relational expression between the virtual channel SNR Γ and the bit error rate BER in a coding mode ENC, and f2−1 represents the inverse operation of f2.

### Claim 8 (depends on 7)

The method according to claim 7, characterized in that the expression f1 is obtained according to theoretical analysis or numerical simulation.

### Claim 9 (depends on 7)

The method according to claim 7, characterized in that the expression f2 is obtained according to theoretical analysis or numerical simulation.

### Claim 10 (depends on 7)

The method according to claim 7, characterized in that the expected bit error rate BER is determined according to the virtual channel SNR Γ and channel eigenvector length L, wherein L is determined by cryptographic key length and quantization mode.

### Claim 11 (depends on 7)

The method according to claim 7, characterized in that the error correction performance of the coding mode ENC is one to two orders of magnitude higher than the expected bit error rate BER.