Subversion Repositories Kolibri OS

;    sshlib_host.inc - SSH remote host authentication

;

;    Copyright (C) 2021 Jeffrey Amelynck

;

;    This program is free software: you can redistribute it and/or modify

;    it under the terms of the GNU General Public License as published by

;    the Free Software Foundation, either version 3 of the License, or

;    (at your option) any later version.

;

;    This program is distributed in the hope that it will be useful,

;    but WITHOUT ANY WARRANTY; without even the implied warranty of

;    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

;    GNU General Public License for more details.

;

;    You should have received a copy of the GNU General Public License

;    along with this program.  If not, see .

; https://datatracker.ietf.org/doc/html/rfc4253#section-6.6

; https://datatracker.ietf.org/doc/html/rfc3447

; https://datatracker.ietf.org/doc/html/rfc4716

proc sshlib_host_verify  con_ptr, str_host_key, str_signature, message, message_len

locals

        current_hkb64           rb MAX_PUBLIC_KEY_SIZE*4        ; Current Host key in Base64

        cached_hkb64            rb MAX_PUBLIC_KEY_SIZE*4        ; Cached Host key in Base64

        key_name_sz             dd ?

        hostname_sz             dd ?

        current_hk64_end        dd ?

endl

        mov     eax, [con_ptr]

        lea     ebx, [eax + sshlib_connection.hostname_sz]

        mov     [hostname_sz], ebx

        cmp     [eax+sshlib_connection.algo_hostkey], SSHLIB_HOSTKEY_RSA

        je      .rsa

        ; ..add more here

        mov     eax, SSHLIB_ERR_HKEY_NO_ALGO

        ret

  .rsa:

        stdcall sshlib_host_verify_rsa, [str_host_key], [str_signature], [message], [message_len]

        test    eax, eax

        jnz     .err

        mov     [key_name_sz], ssh_rsa_sz

  .lookup:

; Convert the current host key to base64

        mov     esi, [str_host_key]

        mov     ecx, [esi]

        bswap   ecx

        add     esi, 4

        lea     edi, [current_hkb64]

        call    base64_encode

        mov     [current_hk64_end], edi

; Try to read the cached key for this host and key type

        lea     edi, [cached_hkb64]

        invoke  ini_get_str, known_hostsfile, [hostname_sz], [key_name_sz], edi, MAX_PUBLIC_KEY_SIZE*4, 0

        test    eax, eax

        jnz     .unknown

; If the cached key is empty, return SSHLIB_HOSTKEY_PROBLEM_UNKNOWN

        lea     esi, [cached_hkb64]

        cmp     byte[esi], 0

        je      .unknown

; Else, compare it to the current one

        lea     edi, [current_hkb64]

        mov     ecx, MAX_PUBLIC_KEY_SIZE*4

  .cmploop:

        lodsb

        scasb

        jne     .mismatch

        test    al, al

        jz      .match

        dec     ecx

        jnz     .cmploop

        jmp     .mismatch

  .match:

        xor     eax, eax

        ret

  .mismatch:

int3

        lea     eax, [current_hkb64]

        stdcall sshlib_callback_hostkey_problem, [con_ptr], SSHLIB_HOSTKEY_PROBLEM_MISMATCH, eax

        cmp     eax, SSHLIB_HOSTKEY_ACCEPT

        je      .store

        ret

  .unknown:

        lea     eax, [current_hkb64]

        stdcall sshlib_callback_hostkey_problem, [con_ptr], SSHLIB_HOSTKEY_PROBLEM_UNKNOWN, eax

        cmp     eax, SSHLIB_HOSTKEY_ACCEPT

        je      .store

        ret

  .store:

        lea     esi, [current_hkb64]

        mov     ecx, [current_hk64_end]

        sub     ecx, esi

        invoke  ini_set_str, known_hostsfile, [hostname_sz], [key_name_sz], esi, ecx

        xor     eax, eax

        ret

  .err:

        ret

endp

; https://datatracker.ietf.org/doc/html/rfc3447#section-8.2.2

; RSASSA-PKCS1-V1_5-VERIFY

proc sshlib_host_verify_rsa str_host_key, str_signature, M, message_len

locals

        h_ctx                   dd ?

; Signer's RSA public key

        mpint_e                 dd ?    ; public exponent

        mpint_n                 dd ?    ; modulus

        mpint_m                 dd ?

        EM                      dd ?

        EM_accent               dd ?

        mpint_s                 dd ?    ; rsa_signature_blob

;        k       dd ?    ; length of RSA modulus n

endl

        DEBUGF  3, "SSH: Performing RSA verification\n"

        mcall   68, 12, sizeof.crash_ctx + 5*(MAX_BITS/8+4)

        test    eax, eax

        jz      .err_nomem

        mov     [h_ctx], eax

        add     eax, sizeof.crash_ctx

        mov     [mpint_e], eax

        add     eax, MAX_BITS/8+4

        mov     [mpint_n], eax

        add     eax, MAX_BITS/8+4

        mov     [mpint_m], eax

        add     eax, MAX_BITS/8+4

        mov     [EM], eax

        add     eax, MAX_BITS/8+4

        mov     [EM_accent], eax

        add     eax, MAX_BITS/8+4

        mov     [mpint_s], eax

;        add     eax, MAX_BITS/8+4

; Host key

        mov     esi, [str_host_key]

        mov     ecx, [esi]

        bswap   ecx

        cmp     ecx, MAX_PUBLIC_KEY_SIZE

        ja      .err_key

; Host key type (string)

        cmp     dword[esi+4], 0x07000000

        jne     .err_key

        cmp     dword[esi+8], 'ssh-'

        jne     .err_key

        cmp     dword[esi+11], '-rsa'

        jne     .err_key

        add     esi, 4+4+7

; mpint e

        stdcall mpint_to_little_endian, [mpint_e], esi

        add     esi, eax

        add     esi, 4

; mpint n

        stdcall mpint_to_little_endian, [mpint_n], esi

;        mov     [k], eax             ;; HMMMM FIXME, 0-byte..

; Signature

        mov     esi, [str_signature]

        mov     ecx, [esi]

        bswap   ecx             ; TODO: check length

; Host key type (string)

        cmp     dword[esi+4], 0x07000000

        jne     .err_signature

        cmp     dword[esi+8], 'ssh-'

        jne     .err_signature

        cmp     dword[esi+11], '-rsa'

        jne     .err_signature

        add     esi, 4+4+7

; RSA signature blob

        stdcall mpint_to_little_endian, [mpint_s], esi

;        cmp     eax, [k]

 ;;;       jne     .err_signature

; RSAVP1

        stdcall mpint_modexp, [mpint_m], [mpint_s], [mpint_e], [mpint_n]

; I2OSP

        stdcall mpint_shrink, [mpint_m]

        stdcall mpint_grow, [mpint_m], 256

        stdcall mpint_to_big_endian, [EM], [mpint_m]

; EMSA-PKCS1-v1_5

        invoke  sha1_init, [h_ctx]

        invoke  sha1_update, [h_ctx], [M], [message_len]

        invoke  sha1_final, [h_ctx]

        mov     edi, [EM_accent]

        mov     al, 0x00

        stosb

        mov     al, 0x01

        stosb

        mov     ecx, 256 - (rsa_sha1_t.len + 3 + SHA1_HASH_SIZE)

        mov     al, 0xff

        rep stosb

        mov     al, 0x00

        stosb

        mov     esi, rsa_sha1_t

        mov     ecx, rsa_sha1_t.len

        rep movsb

        mov     esi, [h_ctx]

        mov     ecx, SHA1_HASH_SIZE

        rep movsb

; Compare EM with EM_accent

        mov     esi, [EM]

        add     esi, 4

        mov     edi, [EM_accent]

        mov     ecx, 256/4

        xor     eax, eax

  .ct_cmp_loop:

        mov     ebx, [esi]

        xor     ebx, [edi]

        or      eax, ebx

        lea     esi, [esi+4]

        lea     edi, [edi+4]

        dec     ecx

        jnz     .ct_cmp_loop

        push    eax

        mcall   68, 13, [h_ctx]

        pop     eax

        test    eax, eax

        jnz     .fail

        DEBUGF  3, "SSH: RSA verification OK!\n"

        ret

  .fail:

        DEBUGF  3, "SSH: RSA verification failed!\n"

        mov     eax, SSHLIB_ERR_HKEY_VERIFY_FAIL

        ret

  .err_nomem:

        mov     eax, SSHLIB_ERR_NOMEM

        ret

  .err_signature:

        mov     eax, SSHLIB_ERR_HKEY_SIGNATURE

        ret

  .err_key:

        mov     eax, SSHLIB_ERR_HKEY_PUBLIC_KEY

        ret

endp

base64_encode:

        xor     ebx, ebx

  .loop:

        lodsb

        call    .byte

        dec     ecx

        jnz     .loop

  .final:

        mov     al, 0

        test    ebx, ebx

        jz      .f000

        call    .byte

        test    ebx, ebx

        jz      .f001

        call    .byte

        mov     byte[edi-2], '='

  .f001:

        mov     byte[edi-1], '='

  .f000:

        mov     byte[edi], 0

        ret

  .byte:

        inc     ebx

        shl     edx, 8

        mov     dl, al

        cmp     ebx, 3

        je      .b001

        ret

  .b001:

        shl     edx, 8

        inc     ebx

  .b002:

        rol     edx, 6

        xor     eax, eax

        xchg    al, dl

        mov     al, [base64_table+eax]

        stosb

        dec     ebx

        jnz     .b002

        ret

iglobal

        known_hostsfile db '/sys/settings/known_hosts.ini', 0

        base64_table    db 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/'

        rsa_sha1_t      db 0x30, 0x21, 0x30, 0x09, 0x06, 0x05, 0x2B, 0x0E, 0x03, 0x02, 0x1A, 0x05, 0x00, 0x04, 0x14

        .len = $ - rsa_sha1_t

        ssh_rsa_sz      db 'ssh-rsa', 0

endg