Speech Hiding Reference: “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: /ICICS Speaker: Chung-Yi Wang Adviser: Quincy Wu Date: 2007/6/4

2007/6/42 outline Introduction Basic Ideals Flow Chart Results Reference

2007/6/43 Introduction(1/3) A speech technique that protects the speech signal from the peeping of illegal users is proposed

2007/6/44 SenderReceiver Network Illegal user SenderReceiver Network

2007/6/45 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…)

2007/6/46 Introduction(3/3) Embedding the secret speech into another speech (cover speech) could be a good solution Stego speech (cover speech with secret speech) is meaningful Illegal users will be perplexed by speech hiding system Even if illegal users detect the Stego speech is fraud… They still can’t obtain the secret speech without the private key since the secret speech is encrypted

2007/6/47 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!

2007/6/48 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

2007/6/49 Basic Ideals(3/4) | Low Frequency Band | | -- High Frequency -- | Hiding data here!

2007/6/410 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!

2007/6/411 Flow chart S C S’’ 1.Compress and Encrypt Ch Cl 2.Sub-band 3.Hidden G 4.Combine G 5.Send Gh Gl 6.Sub-band S’’ 7.Construct S 8.Decode

2007/6/412 Flow chart Process Cover Speech C Fs 1.Sub-band Ch Fs/2 Cl Fs/2 Cl’ Fs/2 2.DPCM or PCM Ch’ Fs/2 Hiding Speech Band

2007/6/413 Flow chart Process Cover Speech Analog Digital DPCMP (Differential Pulse Code Modulation) PCM ( Pulse Code Modulation) Staircase, Finite Compress

2007/6/414 Flow chart Process Secret Speech S Fs 1.Sub-band Sh Fs/2 Sl Fs/2 Sl’ Fs/2 3.DPCM or PCM 2.Drop 1.Noise 2.Reduce bandwidth Sl’’ Fs/2 4.DES or IDEA

2007/6/415 Flow chart Hiding Secret Speech into Cover Speech S’’ … One Speech Sample Ch’ …

2007/6/416 Flow chart Hiding Secret Speech into Cover Speech Cover (Ch’) Speech Sample Secret (Sl’’) Speech Sample Cover (Ch’) Speech Sample Cover (Ch’) Speech Sample Embedding r bits from Sl’’ into Ch’ (to LSB r bits)

2007/6/417 Flow chart Hiding Secret Speech into Cover Speech How many bits need to pick up? n s is the bytes of Sl’’, n s x 8 means the sum bits of Sl’’ n C is the number of samples in C Ch’ has a half of frequency from C, we should count it by n C / 2 m is the number of bits required to store the value of n s

2007/6/418 Flow chart Hiding Secret Speech into Cover Speech For example… n s is 4 n C is 64 m is 16 (bits) … r = [4 * 8 / (64/2) – 16] = 2 (bits)

2007/6/419 Result Hiding Decode

2007/6/420 Result

2007/6/421 Reference A New Speech Hiding Scheme Based upon Sub- Band Coding Sub-Band Coding DES rd rd IDEA ption_Algorithm ption_Algorithm