Let's play with crypto! v2

let’s play with crypto!
Ange Albertini
MetaRheinMainConstructionDays
MRMCD
5-7 september 2014
HS Darmstadt
www.mrmcd.net 2014/09/05

Ange Albertini
reverse engineering &
visual documentations
@angealbertini
ange@corkami.com
http://www.corkami.com

an encrypted file is
not always encrypted

encrypt(file)
an encrypted file is
not always encrypted
random

Let’s take an example: this is a JPEG picture...

AES( )
...if you encrypt it with AES...

… you get this PNG picture...

3DES( )
...and if you decrypt it with Triple DES...

Don’t worry!
I’ll keep it simple...

...because crypto is (too) hard!

HORROR
And this is my usual reaction...

...but I can still have fun with it...

PNG
TrueCrypt
Crypto
...so let’s play together !

AES
Advanced Encryption Standard

1 block (16 bytes)
+
1 key (16 bytes)*
* in the case of AES-128,
so from now on, we’ll say AES for AES-128.

1 block (16 bytes)
+
1 key (16 bytes)
1 block (16 bytes)

a block of text.
+
MySecretKey12345
┐◄n╩i▐☼←∞└╞∙iû╨►
(BF 11 6E CA 69 DE 0F 1B EC C0 C6 F9 69 96 D0 10)

a block of text.
+
MySecretKey12346
gO┼╗ÑëΩcë ▼LÇk╨î
(67 4F C5 BB A5 89 EA 63 89 20 1F 4C 80 6B D0 8C)

a block of text!
+
MySecretKey12345
wε╩▬▄y&↕ú@αùαφ♣O
(77 EE CA 16 DC 79 26 12 A3 40 E0 97 E0 ED 05 4F)

Any change
in the key or input block
gives a completely
different output

we can’t
control the output
the differences are unpredictable

a block of text.
+
MySecretKey12345
encryption
┐◄n╩i▐☼←∞└╞∙iû╨►

a block of text.
decryption
MySecretKey12345
+
┐◄n╩i▐☼←∞└╞∙iû╨►

π╔6I►♣♫Σ♣╝╤→√çφ╡
(E3 C9 36 49 10 05 0E E4 05 BC D1 1A FB 87 ED B5)
decryption
MySecretKey12346
+
┐◄n╩i▐☼←∞└╞∙iû╨►

outwith the encryption key,
we can restore
the original block

without the encryption key,
we can’t do anything
with the encrypted block

“plaintext” and “crypted”
are just names
encryption ⇔ decryption
are just inverse functions

a block of text.
+
MySecretKey12345
decryption
ä/ë-╦7 ↓h│☻⌂μ[←Ñ
(84 2F 89 2D CB 37 00 19 68 B3 02 7F E6 5B 1B A5)

a block of text.
encryption
MySecretKey12345
+
ä/ë-╦7 ↓h│☻⌂μ[←Ñ
(84 2F 89 2D CB 37 00 19 68 B3 02 7F E6 5B 1B A5)

we can decrypt plaintext
we recover the original block via encryption
⇒ we can control encryption output

Recap
● AES encrypts a block
○ we don’t control the output
● an encrypted block can be restored
○ with the encryption key
● encryption ⇔ decryption are just inverse functions
○ we can decrypt plaintext
○ we can recover the original block via encryption
● we can’t control both input and output
○ one, or the other

This is a cow. This is how a users see it.

This is how an expert sees a cow.
It’s still the same cow, but it has some internal structure.

Let’s work with a simplified structure of beef chunks.

If our cow swallows a microSD, it’s still a valid cow!
Even if it contains foreign data, that is tolerated by the system.

Now, let’s look at the Portable Network Graphics format.

Chunk
● The format is made of variable-sized pieces
○ critical or ancillary
● Common high-level structure
○ independent of the content and its interpretation
⇒ Store proprietary information while
⇒ guaranteeing a minimal compatibility

https://www.google.com/images/srpr/logo11w.png
SHA-1 349841408d1aa1f5a8892686fbdf54777afc0b2c
Let’s take a real example, that you may have seen before.

A tool for computer butchers.
(we’ll use it from now on) (’hachoir’ = meatgrinder)

The Google logo, viewed in Hachoir:
a signature, then a sequence of chunks.

x89 P N G r n ^Z n
Compulsory signature at offset 0
● identify the file type
● identify transfer errors
○ x89 : non ASCII (ASCII = [0 - 128])
○ rn then n : different end of line standards
○ ^Z (x1A) : “End Of File”

Chunk
● Common structure:
a. size, on 4 bytes
b. type, made of 4 letters
■ 1st letter: lowercase ⇒ ancillary chunk
c. data
d. checksum
■ CRC32(type + data)
● We can add custom chunks

IHDR chunk: containing image information

IDAT chunk (compressed): pixels values

IDAT after decompression
(FF FF FF 00 = black + 100% transparent)

IEND chunk: End of File (‘s structure)

What comes after IEND is ignored by PNG tools.
(the image is complete)

Recap
Structure:
1. Signature at offset 0
2. Chunks sequence
a. IHDR header
b. IDAT data
c. IEND end

“I know how
Google works!”
Now, you can impress your friends!

ëPNG♪◙→◙ ♪IHDR
(89 50 4E 47 0D 0A 1A 0A 00 00 00 0D 49 48 44 52)
+
MySecretKey12345
:¼N?â?pzILá+?ìgU
(3A AC 4E 10 83 03 70 7A 49 4C A0 DA 0B 8D 67 55)
Encryption breaks the signature.

logo11w.png: PNG image data, 538 x 190, 8-bit/color RGBA, non-interlaced
+
MySecretKey12345
crypted.png: ISO-8859 text, with no line terminators
Without a signature, the encrypted file is invalid.

If we encrypt a PNG,
we don’t get a PNG
the signature is broken and the structure too
(a priori)

How can we encrypt
oogle into uc?k
duckdu
ckgo

How can we control
input and output?

AES works with blocks
How can we use it on a file?

What happens if each block of a file is encrypted independently (ECB mode)

plaintext blocks
ciphertext blocks
In CBC mode, each encryption depends on previous blocks.

The CBC mode
● “Cipher Block Chaining”
○ considered secure
○ we’ll use it from now on
● introduces an Initialization Vector
○ extra parameter
○ arbitrary
○ in practice, it should be unpredictable

key
+
initialization vector
X blocks
X blocks

Relations between blocks and IV
= ENC(IV ^ P1)
C1
* we use the same key for all operations.
*

=
=
ENC(IV ^ P1)
DEC(ENC(IV ^ P1))
C1
DEC(C1)
Decrypt both sides...

=
=
ENC(IV ^ P1)
DEC(ENC(IV ^ P1))
C1
DEC(C1)
it cancels itself

=
=
ENC(IV ^ P1)
IV ^ P1
C1
DEC(C1)

=
=
=
ENC(IV ^ P1)
IV ^ P1
IV ^ P1 ^ P1
C1
DEC(C1)
P1 ^ DEC(C1)
Apply a XOR on both sides...

=
=
=
ENC(IV ^ P1)
IV ^ P1
IV ^ P1 ^ P1
C1
DEC(C1)
P1 ^ DEC(C1)
...it cancels itself

=
=
=
ENC(IV ^ P1)
IV ^ P1
IV
C1
DEC(C1)
P1 ^ DEC(C1)

=
=
=
=
ENC(IV ^ P1)
IV ^ P1
IV
P1 ^ DEC(C1)
C1
DEC(C1)
P1 ^ DEC(C1)
⇒ IV
We get a relation of IV from P1 and C1

IV = P1 ^ DEC(C1)
P1, C1 are the first 16 bytes of our 2 files
once the key k is chosen,
1. decrypt C1
2. apply a XOR with P1
⇒ we get the IV

key
+
initialization vector
X blocks
X blocks
k
IV
Px
Cx

(89 50 4E 47 0D 0A 1A 0A 00 00 00 0D 49 48 44 52)
(89 50 4E 47 0D 0A 1A 0A 00 00 00 0D 49 48 44 52)
k
IV
P1
C1

(89 50 4E 47 0D 0A 1A 0A 00 00 00 0D 49 48 44 52)
(89 50 4E 47 0D 0A 1A 0A 00 00 00 0D 49 48 44 52)
k
IV
P1
C1
IVManipulation!!

(89 50 4E 47 0D 0A 1A 0A 00 00 00 0D 49 48 44 52)
(89 50 4E 47 0D 0A 1A 0A 00 00 00 0D 49 48 44 52)
k
IV
P1
C1
IVManipulation!!
P1 ^ DEC(C1)

IVManipulation!!
r 1ÿ4┼╬ ╕·§{ú)u≡
(72 00 31 98 34 C5 CE 00 B8 FA 15 7B A3 29 75 F0)
(89 50 4E 47 0D 0A 1A 0A 00 00 00 0D 49 48 44 52)
(89 50 4E 47 0D 0A 1A 0A 00 00 00 0D 49 48 44 52)
k
IV
P1
C1

IVManipulation!!
+
r 1ÿ4┼╬ ╕·§{ú)u≡
(72 00 31 98 34 C5 CE 00 B8 FA 15 7B A3 29 75 F0)
(89 50 4E 47 0D 0A 1A 0A 00 00 00 0D 49 48 44 52)
(89 50 4E 47 0D 0A 1A 0A 00 00 00 0D 49 48 44 52)
k
IV
P1
C1

Status
● we control the first cipher block
○ we can get a valid signature
■ and 8 extra bytes
● we control nothing else
○ no valid structure

How can we control
the structure via encryption?

If we encrypt our picture, we get random data.

If we append another picture to this random data...

… we get back our original picture after decryption.
(followed by some different random data)

If we encrypt the final result, we get our first random data,
followed by our target picture.

Pre-decrypt data
● Decrypt our target’s chunks
● Append them to our source file
○ at the start of the next block
(pad if necessary)
○ it’s still valid thanks to the IEND chunk

Status
● We control
○ a bit of the input
○ a bit of the output
● The source file is still valid
○ original source file (valid)
○ followed by decrypted data

How can we control
crypted data ?

We won’t☺
We’ll ask the file format to ignore it.

Adding a standard comment chunk (tEXt type)

The chunk position doesn’t matter.

Adding a completely custom bing chunk.

[warn] Skip parser 'PngFile': First chunk is not header
The header chunk should be the first one.
In practice, it doesn’t matter
(except for Hachoir)

Recap
Adding custom chunks:
● lowercase type
● chunk order doesn’t matter much
⇒ we can add any extra data
in a custom chunk

add a custom chunk to
cover encrypted data
⇒ it will be ignored
⇒ the encrypted file will be valid!

Status
We control after encryption:
● the first block
○ the signature (8 bytes)
○ 8 extra bytes
■ enough to declare a chunk
(4 bytes of size + 4 bytes of type)
● the chunks of the target
○ by decrypting them in advance

“AngeCryption”
with 2 files Source and Target,
● create a Result file
R shows
● S, initially
● T, after AES-CBC(key, IV) encryption

Initial data
We define the key, and the S and T files.
key AngeCryptionKey!
S
T

Initial checks
● S is a PNG
○ the PNG format tolerates appended data
● T is a PNG
○ it allows custom chunks
(at the beginning of the file, right after the signature)
● S fits in a single chunk
○ its size can be encoded in 4 bytes
● AES-128 has a 16 bytes block size
○ big enough to declare a chunk after the signature

Determine the first cipher block
● R starts with P1, from S
● once encrypted, R starts with:
a. an 8 byte PNG signature
b. a custom chunk
■ that covers all the chunks from S
1. S is 14022 bytes, so that’s 14016 bytes of chunks
2. 14016 is encoded 000036c0
■ with a custom type: rmll
lowercase ⇒ ancillary ⇒ ignored
First cipher block of R, C1:
89 P N G r n 1A n 00 00 36 C0 r m l l
Signature ------------- Length ----- Type ------

First plaintext / cipher blocks
First block of R, P1:
89 P N G r n 1A n 00 00 00 0D I H D R
First block of encrypted R, C1:
89 P N G r n 1A n 00 00 36 C0 r m l l

Determine the IV
We have the P1 & C1 blocks, and the key
1. Decrypt C1
2. XOR with P1
We get the IV that will encrypt P1 into C1:
78 D0 02 81 6B A7 C3 DE 88 DE 56 8F 6A 59 1D 06

Craft R
The IV is determined.
● Pad S to the next 16 bytes alignment
● Encrypt via AES-CBC with our parameters
→ with this IV, S will start with:
(after encryption)
1. a signature
2. a rmll chunk (covering the rest of S)

Adjust the custom chunk
1. Chunks end with a CRC32
○ calculate it (using the encrypted data)
2. Append T’s plaintext chunks
3. Decrypt the result
○ after padding

Result
1. signature
2. S chunks
3. padding
4. T chunks
(pre-decrypted)
0000: 89 50 4E 47-0D 0A 1A 0A-00 00 00 0D-49 48 44 52 ëPNG IHDR
0010: 00 00 02 1A-00 00 00 BE-08 06 00 00-00 73 AB A6 + s½ª
0020: F7 00 00 36-8D 49 44 41-54 58 C3 EC-D9 CB 7A D3 ˜ 6ìIDATX+8+-z+
0030: 66 02 C6 71-3A 9D 43 DB-95 9F 67 3A-09 98 10 4C f ¦q:¥C¦òƒg: ÿ L
...
36A0: F5 2D D0 30-33 33 33 BB-C4 3C 04 33-33 33 BB D8 )--0333+-< 333++
36B0: FE 07 A4 AD-F2 BC 37 7B-32 76 00 00-00 00 49 45 ¦ ñ¡=+7{2v IE
36C0: 4E 44 AE 42-60 82 00 00-00 00 00 00-00 00 00 00 ND«B`é..........
36D0: 43 F7 62 F2-4C 6A 07 4D-03 41 82 84-3C D3 F4 39 C˜b=Lj M Aéä<+(9
36E0: FC 27 90 6B-82 71 C8 34-3E 48 4D C1-4C 2A BB 96 n'Ékéq+4>HM-L*+û
36F0: 3C 97 01 67-FE B3 E4 03-E9 09 B2 C3-7E 54 B7 23 <ù g¦¦S T ¦+~T+#
3700: 57 37 3F 1E-DF 67 B3 E8-60 B3 EC A6-CA 51 61 11 W7? ¯g¦F`¦8ª-Qa
...
5CE0: CC 22 8A A0-EC 19 8C DD-26 79 03 29-03 90 93 F1 ¦"èá8 î¦&y ) Éô±
5CF0: 41 CE 4F DB-C0 70 A5 74-D0 74 B7 2E-06 9B 48 7C A+O¦+pÑt-t+. ¢H|
5D00: 2F A6 D1 ED-57 FB 88 67-D1 B0 10 4C-1C 6E CB 15 /ª-fWvêg-¦ L n-

1. signature
2. custom chunk
a. CRC32
3. T chunks
4. padding
Encrypted result
0000: 89 50 4E 47-0D 0A 1A 0A-00 00 36 C0-72 6D 6C 6C ëPNG 6+rmll
0010: 9A 3E 30 1C-F1 D6 E1 41-B7 38 DB A1-5A 71 57 8F Ü>0 ±+ßA+8¦íZqWÅ
0020: 6E 49 A0 D5-76 4C 33 7D-9B CA 44 B8-72 27 48 D9 nIá+vL3}¢-D+r'H+
0030: 64 20 A6 7F-38 D8 89 4A-9F 5F 92 45-17 5D 70 BA d ª8+ëJƒ_ÆE ]p¦
...
36A0: 4D 1E 79 E7-9E F5 81 AC-0C 4C 3B 03-75 43 2B 15 M ytP)ü¼ L; uC+
36B0: B6 9F F4 32-E8 3C 02 67-96 DA 7B 1D-A8 E5 1E BF ¦ƒ(2F< gû+{ ¿s +
36C0: D1 04 25 DF-E5 92 E3 62-30 9A F6 08-60 57 BC 5B - %¯sÆpb0Ü÷ `W+[
36D0: 98 38 F0 D6-00 00 00 0D-49 48 44 52-00 00 00 86 ÿ8=+ IHDR å
36E0: 00 00 00 86-08 02 00 00-00 97 1B 65-C6 00 00 25 å ù e¦ %
36F0: FE 49 44 41-54 78 5E D4-C0 C1 0A 00-10 0C 00 50 ¦IDATx^++- P
3700: FF FF 6F CA-8D B8 A8 95-92 1C 56 0E-36 9B F9 0E o-ì+¿òÆ V 6¢·
...
5CE0: EE 4B 05 D4-46 49 B3 66-30 ED 6E BF-E7 23 7B C9 eK +FI¦f0fn+t#{+
5CF0: C8 D7 51 F8-99 B7 9C 00-00 00 00 49-45 4E 44 AE ++Q°Ö+£ IEND«
5D00: 42 60 82 00-00 00 00 00-00 00 00 00-00 00 00 00 B`é.............

Generalized case
The only requirements:
● The source format tolerates appended data
● The target format can fit a signature and chunk
declaration in a single cipher block
● S fits in a single target format chunk
We can use other algorithms,
both ways (encryption or decryption)
with various file formats (even in the same file)

→
PoC||GTFO 0x3 is a PDF that you can encrypt into a PNG
(and it shows its own IV)

For more information (PDF, JPG, GynCryption, PiP…):
https://speakerdeck.com/ange/when-aes-equals-episode-v
https://www.youtube.com/watch?v=wbHkVZfCNuE

TrueCrypt software
● Creates and manages a virtual storage volume
○ Encrypted
○ Transparent for the system
The volume is useless without the password.

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PE
Standard file format headers

d/Γ↨jôù☺♫Ö▲b¶n0ï
∟RKl♣╟┐l⌂QH┐▐φ♫ö
┬_φ┬Ió£ná→╖G∙♣Σ►
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m←↓ü;·$¿4σ╫áú≈₧
U'k~ù^▒H▄s₧╦êΘμ♦
♠╔,Gδ;åa┤∙NßWπsδ
»Mπ◄=┌G]t +ßQ^l
┴mí≡èτDz╜&╜⌠╨SOî
Vg£ª}ù↓¢┘;4Γ╖á♠┘
ñ▼ö►:♂╠L♦9♂╚╢ÆH(
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░§§É↑â╜ærâp╥xε▲♣
┌Uü╜╫l╪Ñ≥ôùRc∙╠Γ
¡öàx₧╢₧╚f▌Z┘é♪!Ω
L◄±Ä3╬╤ε}:ÇRu╒º¢
▬£÷Cd▼├à·3g~Bêc┌
MΦvεÖ/à╕⌂Ñ9ôΓ≈♫╤
┐╩P┴╥F¥0½╙'*"ú▌◙
¡╔^è¼¶│ÅDN▌♀♂¬↨♠
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Y≡yí#û?♥╞-î§yY¶╖
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Ω╟╬ìPδW9▀8◄Σê♫╨Ω
♦♠Æ►♂r▬╜E╣&╚☻⌠¬░
πa ┐╪å<6▀vMR6₧☻:
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Headers of different TrueCrypt files.

Random contents?
A file format designed not to be identified
● except if you have the password
● random appearance
○ you can deny it’s a TrueCrypt volume
● there is a header
○ but it’s encrypted

TRUE ♣• Iî$B
É ☻ É ☻
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U'k~ù^▒H▄s₧╦êΘμ♦♠╔,Gδ;åa┤∙NßWπsδ
»Mπ◄=┌G]t +ßQ^l┴mí≡èτDz╜&╜⌠╨SOî
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┌Uü╜╫l╪Ñ≥ôùRc∙╠Γ¡öàx₧╢₧╚f▌Z┘é♪!Ω
L◄±Ä3╬╤ε}:ÇRu╒º¢=2ñ∩╝·└¬╝╣♀║æ╘Q╔
Aüμ{w{y◙Æƒom¥↕ú±╣}k▄0○◄↑Ä╪┌&D?í√
╒Z█ jαÆ╙ë{/╗αô.*R←pr(b?▼◄&åÆ▲Θ[É
bÆμA▲ºßÑ∟Θ▀döòêî♪Ω&yá╔☼◘┌╧>▲╓M1*
╦*¡∟☺4Å)▼ôTαÉ÷↔+◙‼M« :▼GF[($nΘ÷Å
▌╣èTΦ▲Sσ■ëOì#÷ô]+◄:f9ôτu╓█B▒♦▬█↕
♫╪(Z⌡▬ñ[< G]≡ÇâΦ╗⌂█∟⌠í<|æ9oΣ║z!L
A TrueCrypt header, before and after decryption.

How many files do you have
that are 100% random?
it’s not so stealthy

Potential volumes detection
● no known header
● “big size”
● size rounded to 512
● random content from the start
○ very high entropy

Just a password?
If encryption only depends on the password,
TrueCrypt is vulnerable to rainbow *
table attacks.
* pre-computed tables (to make faster attacks)

Salt
The file starts with 64 bytes of salt:
● random data
● combined with the password
● used to decrypt the header
⇒ no possible pre-computing
⇒ rainbow tables are useless

d/Γ↨jôù☺♫Ö▲b¶n0ï∟RKl♣╟┐l⌂QH┐▐φ♫ö
┬_φ┬Ió£ná→╖G∙♣Σ►-◄8╓ZX◙nb¶ìMÇx▄Ö
╟ü╪Gñö◙-•╢É}►f~+m←↓ü;·$¿4σ╫áú≈₧
Vg£ª}ù↓¢┘;4Γ╖á♠┘ñ▼ö►:♂╠L♦9♂╚╢ÆH(
L◄±Ä3╬╤ε}:ÇRu╒º¢=2ñ∩╝·└¬╝╣♀║æ╘Q╔
╦*¡∟☺4Å)▼ôTαÉ÷↔+◙‼M« :▼GF[($nΘ÷Å
♫╪(Z⌡▬ñ[< G]≡ÇâΦ╗⌂█∟⌠í<|æ9oΣ║z!L
Ö╚Sâìí°B'⌡♪♀┬Q1■#┐[∟█╝╜x│I╨♦┌½c╪
▬è▄UYÆ/º·╝☻0£MP╔ê¿J♪_>╡∟╢εVRt╣i
ª÷┘FÆ╬C╕μïc┘$☺ƒc»-7JÅï○})ªj♪σ+Θê
↑(Ä╔•é░u_─◙Xm½8▬╫á≤≥╗▬à<↑GÄ≈4Gß¬
↑μ^═Γu╩úC┐☻╟iÆ▀Ñ»FS∟≥■♂╕WCÑ╨ê±²ñ
äδ:ºék╡nÄw╩ßÆ▬!z∞♫ N½Φ╒┼C◘╬ÑÑ ?D
...
Salt
(to decrypt the header)
Header
● crypted with salt and password
● contains the key used to decrypt the volume
Volume
● encrypted with the key in the header
Structure of a TrueCrypt volume

If we modify the salt,
we just have to
to re-crypt the header
no need to change the volume itself
(the volume key hasn’t changed)

Idea:
Integrate a TrueCrypt volume
into another file
- stealthier
- both formats stay valid

Strategy
1. Modify the host to make free space
near the beginning
○ create a custom chunk to contain the volume
2. Copy the header and the volume’s content
○ the decrypted header hasn’t changed,
and the volume hasn’t either
3. Decrypt the header
○ with the initial salt
4. Re-crypt the header
○ with the salt from the start of the host
5. Adjust the CRC of the chunk
○ optional, as the chunk is ancillary

ëPNG♪◙→◙ ♪IHDR ☻→ ╛◘♠ s½ª
≈ 6ìIDATX├∞┘╦z╙f☻╞q:¥C█òƒg:○ÿ►L
τ♠╝₧Æáp╩njB╚üC►▌╡Ñ┼ä╬^wα←h►9┴∞|♣
Eí7α⌡äâÆmí╚w≡═√╔û-┘Æ¡ôc[~▀τ∙»║¬∞
∩╦☼∙ö►Γ¶cî1╞╪ ΓC`î1╞╪`í1i¢yl)▓│e
K│{dUæ!╦?▓jHtvμ'ºÅ₧N °╤Då½◙╥ª←)▓
S∟╟q∟7⌐╦24╬=╢◙¿ä4└┬@&↕N@FúGφ≥☺⌡Ç
åo╙■↓╙☼ ╨æå¶öπ7Éπ8Ä#4╞d│¢⌡┬∞ªU♠,
¬╚D┬i╞º▬4B`#%h◘αó3│ëÅ≥╘├☼E~#9Äπ8
Bcäv~│^☻0*╚DBμ♠F/lDüF←←⌐Cú§á!ª~°
`!↔⌐êo<8Äπ8Bc◘╕PÉÄ¼≤Mx♂•ìx?ƒ♀∟→
¥U%:■±=╤┴q▄Σφïτ▀ΩHx┌wzαm»G╗25|;≈
k|·‼♠ì┬ôz☺i╚ö╕p7Lh♦a#64ⁿ▒! ♪⌠╛èJ
ⁿ╓r∟7◄╚x☺d╝ (:kíπü╖²▲┘αP╗≤çFφï↔ò
╕¢¶h ▬◙╥æpΩä╞∙‼àå5Lh8Y¿é◙ⁿ♠s∟ùI
dⁿ7 ↓/:▐nñ☼ì→"2&☺→↨~«+╚p♥#<4Ω╛╨p
a├D♠╥Ç♀Ö☻`┤╩•♦dáÅeñí◙2É↓ΘτôD╨≡`├
I╛σP°Mμ8.+√ⁿ┼╖:↕v╧♥┌wzαm/á]Ö┌▌Äº
┌τ|ôæ}h|╒♦♠↕Nqá╤±Vúè44░?╚Çàé╩HGμ
○BC|∙¥¥ü◘♫Äπ▓âîôà♠ææuh ↑Ed|σ☻F►4
ⁿ░╤☺♪♂╨╨☺ï╥░■⌂Çè"*ú┌○Aâαα8n2É±<
↓±íAdd↓→ÇE♫Θ↕↑N○áQEÑQ{╞ Fíë♫≤♦áA
pp∟7v√♀╚°∞┼♥ßΘy@√Njw{☺φ╩εw╖s┐åêî
╟ü╪Gñö◙-•╢É}►f~+m←↓ü;·$¿4σ╫áú≈₧
Vg£ª}ù↓¢┘;4Γ╖á♠┘ñ▼ö►:♂╠L♦9♂╚╢ÆH(
L◄±Ä3╬╤ε}:ÇRu╒º¢=2ñ∩╝·└¬╝╣♀║æ╘Q╔
╦*¡∟☺4Å)▼ôTαÉ÷↔+◙‼M« :▼GF[($nΘ÷Å
♫╪(Z⌡▬ñ[< G]≡ÇâΦ╗⌂█∟⌠í<|æ9oΣ║z!L
Ö╚Sâìí°B'⌡♪♀┬Q1■#┐[∟█╝╜x│I╨♦┌½c╪
↑(Ä╔•é░u_─◙Xm½8▬╫á≤≥╗▬à<↑GÄ≈4Gß¬
...
TrueCrypt volume Image

≈ ♦Å╫true
╟ü╪Gñö◙-•╢É}►f~+m←↓ü;·$¿4σ╫áú≈₧
Vg£ª}ù↓¢┘;4Γ╖á♠┘ñ▼ö►:♂╠L♦9♂╚╢ÆH(
L◄±Ä3╬╤ε}:ÇRu╒º¢=2ñ∩╝·└¬╝╣♀║æ╘Q╔
╦*¡∟☺4Å)▼ôTαÉ÷↔+◙‼M« :▼GF[($nΘ÷Å
♫╪(Z⌡▬ñ[< G]≡ÇâΦ╗⌂█∟⌠í<|æ9oΣ║z!L
Ö╚Sâìí°B'⌡♪♀┬Q1■#┐[∟█╝╜x│I╨♦┌½c╪
↑(Ä╔•é░u_─◙Xm½8▬╫á≤≥╗▬à<↑GÄ≈4Gß¬
...
Create free space in the file to host the volume.

╟ü╪Gñö◙-•╢É}►f~+m←↓ü;·$¿4σ╫áú≈₧
Vg£ª}ù↓¢┘;4Γ╖á♠┘ñ▼ö►:♂╠L♦9♂╚╢ÆH(
L◄±Ä3╬╤ε}:ÇRu╒º¢=2ñ∩╝·└¬╝╣♀║æ╘Q╔
╦*¡∟☺4Å)▼ôTαÉ÷↔+◙‼M« :▼GF[($nΘ÷Å
♫╪(Z⌡▬ñ[< G]≡ÇâΦ╗⌂█∟⌠í<|æ9oΣ║z!L
Ö╚Sâìí°B'⌡♪♀┬Q1■#┐[∟█╝╜x│I╨♦┌½c╪
↑(Ä╔•é░u_─◙Xm½8▬╫á≤≥╗▬à<↑GÄ≈4Gß¬
...
≈ ♦Å╫true
╟ü╪Gñö◙-•╢É}►f~+m←↓ü;·$¿4σ╫áú≈₧
Vg£ª}ù↓¢┘;4Γ╖á♠┘ñ▼ö►:♂╠L♦9♂╚╢ÆH(
L◄±Ä3╬╤ε}:ÇRu╒º¢=2ñ∩╝·└¬╝╣♀║æ╘Q╔
╦*¡∟☺4Å)▼ôTαÉ÷↔+◙‼M« :▼GF[($nΘ÷Å
♫╪(Z⌡▬ñ[< G]≡ÇâΦ╗⌂█∟⌠í<|æ9oΣ║z!L
Ö╚Sâìí°B'⌡♪♀┬Q1■#┐[∟█╝╜x│I╨♦┌½c╪
↑(Ä╔•é░u_─◙Xm½8▬╫á≤≥╗▬à<↑GÄ≈4Gß¬
...
⇒
Copy the volume in the created space.

╟ü╪Gñö◙-•╢É}►f~+m←↓ü;·$¿4σ╫áú≈₧
Vg£ª}ù↓¢┘;4Γ╖á♠┘ñ▼ö►:♂╠L♦9♂╚╢ÆH(
L◄±Ä3╬╤ε}:ÇRu╒º¢=2ñ∩╝·└¬╝╣♀║æ╘Q╔
╦*¡∟☺4Å)▼ôTαÉ÷↔+◙‼M« :▼GF[($nΘ÷Å
♫╪(Z⌡▬ñ[< G]≡ÇâΦ╗⌂█∟⌠í<|æ9oΣ║z!L
Ö╚Sâìí°B'⌡♪♀┬Q1■#┐[∟█╝╜x│I╨♦┌½c╪
↑(Ä╔•é░u_─◙Xm½8▬╫á≤≥╗▬à<↑GÄ≈4Gß¬
...
≈ ♦Å╫true
TRUE ♣• Iî$B
É ☻ É ☻
C¬α╔Ñ«ÑêI█⌠▬♀D╣▼xΦm↓¬0τzP°W5»╣Fc
Jl¼∙L¢▒9Oä°τEpó&←╠¿oμÆ☺▬ìä5Θä↨_○
¼I┐¡
Ö╚Sâìí°B'⌡♪♀┬Q1■#┐[∟█╝╜x│I╨♦┌½c╪
↑(Ä╔•é░u_─◙Xm½8▬╫á≤≥╗▬à<↑GÄ≈4Gß¬
...
Decrypt the header with the volume’s salt.

╟ü╪Gñö◙-•╢É}►f~+m←↓ü;·$¿4σ╫áú≈₧
Vg£ª}ù↓¢┘;4Γ╖á♠┘ñ▼ö►:♂╠L♦9♂╚╢ÆH(
L◄±Ä3╬╤ε}:ÇRu╒º¢=2ñ∩╝·└¬╝╣♀║æ╘Q╔
╦*¡∟☺4Å)▼ôTαÉ÷↔+◙‼M« :▼GF[($nΘ÷Å
♫╪(Z⌡▬ñ[< G]≡ÇâΦ╗⌂█∟⌠í<|æ9oΣ║z!L
Ö╚Sâìí°B'⌡♪♀┬Q1■#┐[∟█╝╜x│I╨♦┌½c╪
↑(Ä╔•é░u_─◙Xm½8▬╫á≤≥╗▬à<↑GÄ≈4Gß¬
...
≈ ♦Å╫true
┤♣▒εÜ┘$φ╗3☼»αG↔öÇ═0₧:P╞!•▒áwó░«
u∟╔AL╙J<►Φs L╣I▌èαè3l?WÑû╠♠ìΣ}⌂
n°ôaîlö§╔ó¢i∞¬∩╦8≡)≤Çg╘╩┴3ëΓ%◄/(
b☻▬↔‼⌐j☻♥dæ╧↔ä♪┘┬ì §(▒┌:╞ùxº╟║∞◄
á◄Å±n≤ó± ►¶Jp/♀α/♠P☼zz(≤ÿ╩↔ï┼§•ô
,∟+╙aμ─CΩ⌐‼÷α░s╕Å':òφw≡O»♀1▓z♣&ñ
y╔╕à"IX≤▄ⁿJ♣║PÑnö¿╣τ┴7à&ªü>¬ï║Wx
w^╚>à►mtûσf√•wâ╗╥²┼xÿáôùε▄ôτô≤█≥
╩┌Aj≤⌐¢╟╬M┬ûí δτ╩~⌐Pl¶¼┌╢!zWÅuδ$
/≥Ñw╒V♀WR┤V╥°╔═√=¼7°²√▲┼kd√Fösùc
█◘k├o¬åù♂r╢§F╙◘≥|MÖP;@∞↑xäεù→æ½
r♦«▐R≥óå2♦ô&═τ'5$¼♫π╥÷èzef¥Uí`∙j
╪'¬├Rö`ÿ¶óB≤╪2⌠↑RmâÖ▐¡╝→‼pò[│k«╗
å;·L→pÜ│bzÖ=b¬S~û|¶¿î╩G╢ç╖¼ ‼«ö♠
Ö╚Sâìí°B'⌡♪♀┬Q1■#┐[∟█╝╜x│I╨♦┌½c╪
↑(Ä╔•é░u_─◙Xm½8▬╫á≤≥╗▬à<↑GÄ≈4Gß¬
...
Encrypt the header with the salt from the host.

≈ ♦Å╫true
┤♣▒εÜ┘$φ╗3☼»αG↔öÇ═0₧:P╞!•▒áwó░«
u∟╔AL╙J<►Φs L╣I▌èαè3l?WÑû╠♠ìΣ}⌂
n°ôaîlö§╔ó¢i∞¬∩╦8≡)≤Çg╘╩┴3ëΓ%◄/(
b☻▬↔‼⌐j☻♥dæ╧↔ä♪┘┬ì §(▒┌:╞ùxº╟║∞◄
á◄Å±n≤ó± ►¶Jp/♀α/♠P☼zz(≤ÿ╩↔ï┼§•ô
,∟+╙aμ─CΩ⌐‼÷α░s╕Å':òφw≡O»♀1▓z♣&ñ
y╔╕à"IX≤▄ⁿJ♣║PÑnö¿╣τ┴7à&ªü>¬ï║Wx
w^╚>à►mtûσf√•wâ╗╥²┼xÿáôùε▄ôτô≤█≥
╩┌Aj≤⌐¢╟╬M┬ûí δτ╩~⌐Pl¶¼┌╢!zWÅuδ$
/≥Ñw╒V♀WR┤V╥°╔═√=¼7°²√▲┼kd√Fösùc
█◘k├o¬åù♂r╢§F╙◘≥|MÖP;@∞↑xäεù→æ½
r♦«▐R≥óå2♦ô&═τ'5$¼♫π╥÷èzef¥Uí`∙j
╪'¬├Rö`ÿ¶óB≤╪2⌠↑RmâÖ▐¡╝→‼pò[│k«╗
å;·L→pÜ│bzÖ=b¬S~û|¶¿î╩G╢ç╖¼ ‼«ö♠
Ö╚Sâìí°B'⌡♪♀┬Q1■#┐[∟█╝╜x│I╨♦┌½c╪
↑(Ä╔•é░u_─◙Xm½8▬╫á≤≥╗▬à<↑GÄ≈4Gß¬
...
Sal
TrueCrypt PNG
Header
Volume’s content
End of volume
Image (ignored)
Signature + header
Chunk declaration
Chunk data
Chunk end
Original chunks

TrueCrypt volumes in standard files
(still useable and modifiable)

Conclusion 1/2
● We can add extra data in a standard binary file
● This data can be:
○ another standard file, after en/decryption
○ a TrueCrypt volume

Conclusion 2/2
● No need to understand everything
to have fun with crypto
● Better progress step by step
○ ask an expert
○ hard to debug
● Encrypted doesn’t mean random
● examples: http://bit.ly/1n63yKP
(http://corkami.googlecode.com/svn/trunk/src/angecryption/rmll)

Acknowledgments
@veorq @doegox @iamreddave
@miaubiz @travisgoodspeed @sergeybratus
@cynicalsecurity @rantyben @thegrugq
@skier_t @jvanegue @kaepora @munin
@joernchen @andreasdotorg @tabascoeye
@cryptax @pinkflawd @push_pnx @gynvael
@rfidiot @cbrocas @kennwhite...

@angealbertini
corkami.com
Damn, that's the second time those alien bastards shot up my ride!

Let's play with crypto! v2

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