Example of using TLS-Library parts for generating PRNG numbers

Thu Jul 05, 2018 4:59 pm

Kolibri TLS library --- GitHub repository

If you just want to get this RNG (not interested about how I got it by myself),
just scroll down to " 3) Include this RNG to your project " part of this message!

1) Extract the RNG from TLS Library

Spoiler:

[*][/b] Download three files from this repository:

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hmac.inc  PRF.inc  SHA256.INC

and put them inside a new TLS-Library-RNG subdirectory of your project

[*][/b] Open hmac.inc, you will see this code at lines 41-42

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b = 64 ; block_size
l = 32 ; output length for SHA256

prf function will generate ( b + 3 * l ) random bytes, but only if ( b >= l ) - if this condition is not valid, your project will crash with exception 0E (page fault)

For example, if you want to generate 68 random bytes, you could change these values to

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b = 32 ; block_size
l = 12 ; output length for SHA256

, because ( 32 + 3 * 12 ) = ( 32 + 36 ) = 68

[*][/b] Open SHA256.INC and remove (or comment with ";") these six lines:

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Line  4 || iglobal
Line  5 || align 4
Line 26 || eng
Line 28 || uglobal
Line 29 || align 4
Line 34 || eng

, because if you don't remove these six lines - you will get the errors like undefined symbol 'sha256_start_digest'

2) Get entropy for PRNG and create the interface to it

[*][/b] Copy the source code of get_entropy function from the first post of this thread - (rus) Functions-"sources of entropy" for a quality RNG
(code hidden under a spoiler, click "Show") and put it to a new ./TLS-Library-RNG/entropy.inc file with your functions

Also, you may need to add this code to the end of get_entropy function (before the popa)

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    mov esi, entropy
    mov ebx, ENTROPY_SIZE
    call replace_00_with_ff

, and declare replace_00_with_ff function with this code:

Spoiler:

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; replace_00_with_ff:
; replace 00 with ff in a memory area
;
; IN:    ESI - pointer to a memory area
;        EBX - size of a memory area

replace_00_with_ff:

    push eax ecx

    xor ecx, ecx

    .cycle_replace_00_with_ff:

        cmp byte[esi], 0
        jne .not_00
        mov byte[esi], 0xff

    .not_00:

        inc esi
        inc ecx
        cmp ecx, ebx
        jb .cycle_replace_00_with_ff

    pop ecx eax

    ret

[*][/b] For convenience, to the same entropy.inc file we could add fill_random_buffer interface function:

Spoiler:

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; Prepare, then call a Pseudo Random function based on HMAC

fill_random_buffer:

    pusha

    call get_entropy
    xor ebx, ebx
    xor edx, edx
    xor eax, eax
    xor esi, esi
    stdcall prf, entropy, ENTROPY_SIZE+1, random_buffer

    popa

    ret

+1 at the ENTROPY_SIZE+1 is because the real size of entropy is +1 because of a null character

Also add there convert_random_buffer_to_ascii function - it could convert a part of random buffer to ASCII chars:

Spoiler:

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; convert_random_buffer_to_ascii:
; convert a part of random buffer to ASCII chars
;
; IN:       ECX = size of a part of random buffer which will be converted

convert_random_buffer_to_ascii:

    push esi edx ebx eax

    cmp ecx, 1
    jb .wrong_part_size
    cmp ecx, RANDOM_BUFFER_SIZE
    ja .wrong_part_size

    xor eax, eax
    xor ebx, ebx

    mov esi, random_buffer
    mov edx, 95

  .cycle_conversion:

    mov al, byte[esi]

    cmp al, 95
    jb .skip_division

    div dl
    mov al, ah

  .skip_division:

    add al, 32
    mov byte[esi], al

    inc ebx
    inc esi

    cmp ebx, ecx
    jne .cycle_conversion

  .wrong_part_size:

    pop eax ebx edx esi

    ret

3) Include this RNG to your project

[*][/b] Add this code to your main project file, e.g. to example.asm :

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include "./TLS-Library-RNG/hmac.inc"
include "./TLS-Library-RNG/PRF.inc"
include "./TLS-Library-RNG/SHA256.INC"
include "./TLS-Library-RNG/entropy.inc"

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RANDOM_BUFFER_SIZE = b + 3 * l ; 'b' and 'l' are defined at hmac.inc
                               ; currently, b = 32 and l = 12, so:
                               ;         RANDOM_BUFFER_SIZE = (b + 3 * l) = (32 + 3 * 12) = 68
RANDOM_BUFFER_SIZE_TO_CONVERT = 65; call convert_random_buffer_to_ascii to convert 65 random_bytes to ASCII
                               ; ^ should be smaller than or equal to RANDOM_BUFFER_SIZE
random_buffer        db RANDOM_BUFFER_SIZE dup(0)

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ENTROPY_SIZE = 56 ; check if there are any updates for ENTROPY_SIZE at this "sources of entropy" thread
entropy        db ENTROPY_SIZE dup(255), 0 ; http://board.kolibrios.org/viewtopic.php?f=2&t=3735
                                           ; ( code hidden under a spoiler, click "Show" )

4) Usage of PRNG

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        push    ecx
        call    fill_random_buffer
        mov     ecx, RANDOM_BUFFER_SIZE_TO_CONVERT
        call    convert_random_buffer_to_ascii
        pop     ecx

5) Attached files (with SHA256 checksums)

Prepared TLS-Library-RNG_with_example is attached below to save your time!

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b8d8c04dca25107a17ecbbc800cf4a2dfa923873e3a7bcf247aeb342b9c49ecc  ./entropy.inc
c2d36b18a460e664eec63d5373a3419f5a659379405dc942b1563dacea8f2303  ./example.asm
2a781b30ce74031e2aa37cf8d97a3a60fdf1630f04ef963023e5d20935a3015a  ./TLS-Library-RNG_with_example.zip
0ede9e511fc10f05a11b992808a893b315604b25bbccbd10759202788013cec3  ./TLS-Library-RNG.zip

Includes TLS-Library-RNG directory with four files, and example.asm which can't be compiled separately but you could borrow its' elements

Example of using TLS-Library parts for generating PRNG numbers

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