Speech HidingReference: “A New Speech Hiding Scheme Based upon Sub-Band Coding”

Chin-Chen Chang; Richard Char-Tung Lee; Guang-Xue Xiao; Tung-Shou Chen Digital Object Identifier: 10.1109/ICICS.2003.1292605

Speaker: Chung-Yi WangAdviser: Quincy WuDate: 2007/6/4

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outline

Introduction Basic Ideals Flow Chart Results Reference

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Introduction(1/3)

A speech technique that protects the speech signal from the peeping of illegal users is proposed

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Sender ReceiverNetwork

Illegal user

Sender ReceiverNetwork

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Introduction(2/3) Maybe Cryptosystem is not the best solution

Encrypting data make signal be chaotic and meaningless

Chaotic and meaningless signal always be detected by illegal user They want to break it!

Encrypting Data

(DES,AES,IDEA…)

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Introduction(3/3)

Embedding the secret speech into another speech (cover speech) could be a good solution Stego speech (cover speech with secret speech) i

s meaningful Illegal users will be perplexed by speech hiding syste

m Even if illegal users detect the Stego speech is fra

ud… They still can’t obtain the secret speech without the pri

vate key since the secret speech is encrypted

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Basic Ideals(1/4)

For speech signal, small distortions make difference to human ears

If we could hiding speech but make distortions be small, there is no difference to human ears!

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Basic Ideals(2/4)

Speech signal could divide into two band, the high frequency band and low frequency band

High frequency band always is noise alike to human ears

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Basic Ideals(3/4)

| ------------------------- Low Frequency Band ------------------------ | | -- High Frequency -- |

Hiding data here!

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Basic Ideals(4/4)

Small distortions make difference to human ears Hiding speech but be no difference to human

ears High frequency band always is noise alike to

human ears Hiding data here!

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Flow chart

S

C

S’’

1.Compress and Encrypt

Ch

Cl

2.Sub-band

3.Hidden

G

4.Combine

G5.Send

Gh

Gl

6.Sub-band

S’’

7.Construct

S8.Decode

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Flow chart Process Cover Speech

CFs

1.Sub-band

ChFs/2

ClFs/2

Cl’Fs/2

2.DPCM or PCM

Ch’Fs/2

Hiding Speech Band

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Flow chart Process Cover Speech

Analog

Digital

DPCMP (Differential Pulse Code Modulation)

PCM (Pulse Code Modulation)

Staircase, Finite

Compress

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Flow chartProcess Secret Speech

SFs

1.Sub-band

ShFs/2

SlFs/2

Sl’Fs/2

3.DPCM or PCM

2.Drop

1.Noise

2.Reduce bandwidth

Sl’’Fs/24.DES or IDEA

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Flow chart Hiding Secret Speech into Cover Speech

0 1 2 3 4S’’ …

0123456789101112131415One

Speech Sample

0 1 2 3 4Ch’ …

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Flow chart Hiding Secret Speech into Cover Speech

0123456789101112131415Cover (Ch’)

Speech Sample

0123456789101112131415Secret (Sl’’)

Speech Sample

0123456789101112131415Cover (Ch’)

Speech Sample

0123456789101112131415Cover (Ch’)

Speech Sample

Embedding r bits from Sl’’ into Ch’

(to LSB r bits)

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Flow chart Hiding Secret Speech into Cover Speech

How many bits need to pick up?

ns is the bytes of Sl’’, ns x 8 means the sum bits of Sl’’ nC is the number of samples in C

Ch’ has a half of frequency from C, we should count it by nC / 2

m is the number of bits required to store the value of ns

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Flow chart Hiding Secret Speech into Cover Speech

For example… ns is 4

nC is 64

m is 16 (bits)

0123456789101112131415

16

0 1 2 3 4 … 3164

r = [4 * 8 / (64/2) – 16]

= 2 (bits)

4

0123456789101112131415

0123456789101112131415

0123456789101112131415

0123456789101112131415

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Result

Hiding

Decode

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Result

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Reference A New Speech Hiding Scheme Based upon Sub-Ba

nd Coding http://ieeexplore.ieee.org/iel5/9074/28789/01292605.pdf

Sub-Band Codinghttp://en.wikipedia.org/wiki/Sub-band_coding

DEShttp://en.wikipedia.org/wiki/Data_Encryption_Standard

IDEAhttp://en.wikipedia.org/wiki/International_Data_Encryption_Algorithm