1. Privacy-Preserving Reversible Watermarking for Data Exfiltration Prevention Through Lexicographic Permutations
Source: IIH-MSP(2018):
Authors: Ching-Chun Chang and Chang-Tsun Li
Speaker: Jiang-Yi Lin
Date:

2. Outline Introduction Related Works Proposed scheme
Experimental results
Conclusions

3. Introduction (1/3) – Reversible data hiding in encrypted image (RDHEI)
Encryption Key 𝐾 𝑒
Embedding Key 𝐾 𝑟
Encrypt the image
Embedding
Original image m
Marked image
Key 𝐾 𝑒
Secret data extraction
Key 𝐾 𝑟
Image recover & Secret data extraction
𝐾 𝑒 , 𝐾 𝑟

4. Introduction (2/3) – Vacating room before Encryption
Encryption Key 𝐾 𝑒
Embedding Key 𝐾 𝑟
Encrypt the image
Embedding
Vacating room
Original image m
Marked image
Key 𝐾 𝑒
Secret data extraction
Key 𝐾 𝑟
Image recover & Secret data extraction
𝐾 𝑒 , 𝐾 𝑟

5. Introduction (3/3) – Vacating room after Encryption
Encryption Key 𝐾 𝑒
Embedding Key 𝐾 𝑟
Vacating room
Encrypt the image
Embedding
Original image m
Marked image
Key 𝐾 𝑒
Secret data extraction
Key 𝐾 𝑟
Image recover & Secret data extraction
𝐾 𝑒 , 𝐾 𝑟

6. Related work(1/1)- Lexicographic Permutations
1. Given an original sequence: {12, 1, 7}
2. Permute the original sequence and sort permutation lexicons.
3. For watermark encoding, substitute {12,1,7} with a sorted lexicon {7, 1, 12} to encode the digit ‘2’.
{1, 7, 12}: 0
{1, 12, 7}: 1
{7, 1, 12}: 2
{7, 12, 1}: 3
{12, 1, 7}: 4
{12, 7, 1}: 5

7. Proposed scheme (1/8)-embedding
Create the original sequence by the low nybbles of a pixel pair from the encrypted image.
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174 = ( )2, low nybble: (1110)2 = 14
85 = ( )2, low nybble: (0101)2 = 5
Original sequence: {14, 5} from (174, 85)
Permutation lexicons : {5, 14}: 0
{14, 5}: 1
Pixels at the black positions are modifiable in terms of their low nybbles, whereas those at the white positions are unmodifiable.

8. Proposed scheme (2/8) -embedding
To embed bit 0, substitute the lexicon {14, 5} with {5, 14}
by modifying the low nybbles of the pixel pair.
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Encrypted image
165 = ( )2, low nybble: (0101)2 = 5
94 = ( )2, low nybble: (1110)2 = 14
So the original (174, 85) has been changed to (165, 94).

9. Proposed scheme (3/8)-Extraction
According to the Lexicographic order, the secret bit can be error-free extracted.
Encrypted image
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Encrypted image
165 = ( )2, low nybble: (0101)2 = 5
94 = ( )2, low nybble: (1110)2 = 14
Lexicographic order: 0
The embedded bit: 0
Low nybbles: {5, 14}

10. Proposed scheme (4/8) -Extraction
Step 1: Receiver restores two candidate encrypted images.
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Low nybbles: {14, 5}
174 = ( )2
85 = ( )2,
Low nybbles: {5, 14}
165 = ( )2
94 = ( )2
Encrypted image 1
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Encrypted image 2

11. Proposed scheme (5/8) -Extraction
Step 2: Decrypt two candidate images using the decryption key(same as the encryption key).
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12. Proposed scheme (6/8) -Extraction
Step 3: A content-adaptive estimation is designed for assisting host pixel recovery.
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Candidate
image 1
Origin
version
Error = Sum(|{100,118} – {99,119}|) = Sum({1,1}) = 2
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Candidate
image 2
Error = Sum(|{91,127} – {99,119}|) = Sum({8,8}) = 16

13. Proposed scheme (7/8)-Predictor

14. Proposed scheme (8/8)- Enhance distinction
Low nybbles: {5, 4}
85 = ( )2
84 = ( )2,
Low nybbles: {4, 5}
84 = ( )2
85 = ( )2
Low nybbles: {5, 4}
85 = ( )2
84 = ( )2
Extraction
Pixels={85,84}.
e={5, 4}, N=16. p={3,7},q={11,7}. Suppose secret bit w=0.
pu is coprime to N
e'={5*7, 4*7} (mod N) = {35, 28} (mod N) ={3, 12}.
Since w=0, e'={3, 12} keep intact.
In the extraction phase.
e'={3, 12} => w=0.
For any permutations of e’
G = {{3, 12}*q0, {3, 12}*q1}={{1,4},{5,4}}
GB={{1,4},{5,4}}
Thus, candidate pixels={81,84} or {85,84}
G0={3, 12}*11 (mod N) ={33, 132} (mod N) ={1,4}
G1={3, 12}*7 (mod N) ={21,84} (mod N) ={5,4}
{4, 5}: 0
{5, 4}: 1
{3, 12}: 0
{12, 3}: 1

15. Experimental results (1/2)

16. Experimental results (2/2)

17. CONCLUSIONS Utilize the Lexicographic Permutations for RDHEI.
A Content-Adaptive Estimator for Prediction.
Enhance Distinction.

18. Thank you for listening!