$ xxd file1 |head -n1
00000000: 4b65 6570 206d 6520 706c 6561 7365 135b  Keep me please.[

$ xxd file2 |head -n1
00000000: 4b65 6570 206d 6520 746f 6f50 2f4b 2a77  Keep me tooP/K*w

'F0llow_7he_White_R4bbit\x00'

$ ./step1.bin file1 F0llow_7he_White_R4bbit 2> file1_decrypted.out.b64
Would you like some wine?

$ base64 -d file1_decrypted.out.b64 > file1_decrypted.out
$ file file1_decrypted.out
file1_decrypted.out: RIFF (little-endian) data, AVI, 1280 x 820, ~24 fps,
video: FFMpeg MPEG-4, audio: MPEG-1 Layer 3 (stereo, 44100 Hz)

$ mkdir file1-frames/
$ ffmpeg -i file1_decrypted.out file1-frames/frame%05d.png
$ ./file1_extract_framehex.py
$ file file1_framehex.out
file1_framehex.out.bin: ELF 64-bit LSB executable, x86-64, version 1 (SYSV),
dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, for GNU/Linux
2.6.24, BuildID[sha1]=796e8cb3fec1f948780986af22fbd1348c3db003, stripped

$ ./file1_framehex.out file1_decrypted.out Have_you_guessed_the_riddle_yet 2> file1_video_payload.out
Curiouser and curiouser!
$ file file1_video_payload.out
file1_video_payload.out: RIFF (little-endian) data, WAVE audio, Microsoft PCM, 16 bit, stereo 44100 Hz

The first part of the password is "Use_me_to_d3crypt_". It can be used to
decrypt the next step. But, before using it, have you find the second part?

Congratulation for finding me !

The second part of the password is "the_last_3ncrypted_file"
It can be used to decrypt the next step.
@<;;

$ ./step1.bin file2 Use_me_to_d3crypt_the_last_3ncrypted_file 2> file2_decrypted.out.b64
Begin at the beginning, and go on till you come to the end: then stop.

$ base64 -d < file2_decrypted.out.b64 > file2_decrypted.out
$ file file2_decrypted.out
file2_decrypted.out: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV),
statically linked, BuildID[sha1]=8c36a356734d8731a544c3d66f2eafc2d25475de, stripped

$ ./file2_decrypted.out
Usage: ./chall.bin <pass>
$ ./file2_decrypted.out '<pass>'
Wait please...
Oh my ears and whiskers. You are completely wrong :(

watch *0x080754FD if $pc >= 0x80753F9
commands
break *0x080754FD
continue
end
r pass

Starting program: /tmp/chall5/file2_decrypted.out pass
Wait please...

Hardware watchpoint 1: *0x080754FD

Old value = -419722244
New value = -419722923
0x080753fb in ?? ()
=> 0x080753fb:    83 c2 04    add    $0x4,%edx
Breakpoint 2 at 0x80754fd

Hardware watchpoint 1: *0x080754FD

Old value = -419722923
New value = -2082109099
0x080753fb in ?? ()
=> 0x080753fb:    83 c2 04    add    $0x4,%edx
Breakpoint 3 at 0x80754fd

Breakpoint 2, 0x080754fd in ?? ()
=> 0x080754fd:    55    push   %ebp

dump memory file2_clear.out 0x8048000 0x807b000

//Note: All variables are unsigned 32 bit and wrap modulo 2^32 when calculating
var int[64] s, K

//s specifies the per-round shift amounts
s[ 0..15] := { 7, 12, 17, 22,  7, 12, 17, 22,  7, 12, 17, 22,  7, 12, 17, 22 }
s[16..31] := { 5,  9, 14, 20,  5,  9, 14, 20,  5,  9, 14, 20,  5,  9, 14, 20 }
s[32..47] := { 4, 11, 16, 23,  4, 11, 16, 23,  4, 11, 16, 23,  4, 11, 16, 23 }
s[48..63] := { 6, 10, 15, 21,  6, 10, 15, 21,  6, 10, 15, 21,  6, 10, 15, 21 }

// K[0..27] differs with MD5. It is at .text:08075A5B
K[0..63] := {
    0x14F02B43, 0x89C0E4CA, 0x2EE6E47B, 0x177ECEBF,
    0xA20C3D34, 0x5124C3C0, 0x1AEEF40C, 0x31675B41,
    0xCDB50C26, 0xF0789AA0, 0xFB54C0D4, 0xD58AD882,
    0x393E1CD7, 0x04BD0A4B, 0x28C0426E, 0xCA5F186C,
    0xC662BCD1, 0x0F06B131, 0x5A70DAF6, 0x7A7FF510,
    0x7829CDD8, 0xA1EB40D7, 0xDB2A8729, 0xB51A8A3D,
    0xD84E797A, 0xCC1F406D, 0xE182486D, 0x26E4F7DD,
// from K[28..31], the arrays are the same:
    0xA9E3E905, 0xFCEFA3F8, 0x676F02D9, 0x8D2A4C8A,
    0xFFFA3942, 0x8771F681, 0x6D9D6122, 0xFDE5380C,
    0xA4BEEA44, 0x4BDECFA9, 0xF6BB4B60, 0xBEBFBC70,
    0x289B7EC6, 0xEAA127FA, 0xD4EF3085, 0x04881D05,
    0xD9D4D039, 0xE6DB99E5, 0x1FA27CF8, 0xC4AC5665,
    0xF4292244, 0x432AFF97, 0xAB9423A7, 0xFC93A039,
    0x655B59C3, 0x8F0CCC92, 0xFFEFF47D, 0x85845DD1,
    0x6FA87E4F, 0xFE2CE6E0, 0xA3014314, 0x4E0811A1,
    0xF7537E82, 0xBD3AF235, 0x2AD7D2BB, 0xEB86D391,
}

//Initialize variables with custom constants
var int a0 := 0xFD45F22F   //A
var int b0 := 0x1431EE0C   //B
var int c0 := 0x1458EF65   //C
var int d0 := 0x455684AA   //D

//Pre-processing: adding a single 1 bit
append "1" bit to message
//Pre-processing: padding with zeros
append "0" bit until message length in bits ≡ 448 (mod 512)
append original length in bits mod (2 pow 64) to message

//Process the message in successive 512-bit chunks:
for each 512-bit chunk of message
    break chunk into sixteen 32-bit words M[j], 0 ≤ j ≤ 15
//Initialize hash value for this chunk:
    var int A := a0
    var int B := b0
    var int C := c0
    var int D := d0
//Main loop:
    for i from 0 to 63
        if 0 ≤ i ≤ 15 then
            F := (B and C) or ((not B) and D)
            g := i
        else if 16 ≤ i ≤ 31
            F := (D and B) or ((not D) and C)
            g := (5×i + 1) mod 16
        else if 32 ≤ i ≤ 47
            F := B xor C xor D
            g := (3×i + 5) mod 16
        else if 48 ≤ i ≤ 63
            F := C xor (B or (not D))
            g := (7×i) mod 16
        dTemp := D
        D := C
        C := B
        B := B + leftrotate((A + F + K[i] + M[g]), s[i])
        A := dTemp
    end for
//Add this chunk's hash to result so far:
    a0 := a0 + A
    b0 := b0 + B
    c0 := c0 + C
    d0 := d0 + D
end for

var char digest[16] := a0 append b0 append c0 append d0 //(Output is in little-endian)

//leftrotate function definition
leftrotate (x, c)
    return (x << c) binary or (x >> (32-c));

$ ./file2_decrypted.out bunnyrabbit
Wait please...
Congratulation! You found the White Rabbit!

      ***
     ** **
    **   **
    **   **         ****
    **   **       **   ****
    **  **       *   **   **
     **  *      *  **  ***  **
      **  *    *  **     **  *
       ** **  **  **       **
       **   **  **
      *           *
     *             *
    *    0     0    *
    *   /   @   \   *
    *   \__/ \__/   *
      *     W     *
        **     **
          *****

The flag is the sha256sum of the password.
Send it (and your write-up if you have one) to merenwen@hackinparis.com