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I am researching an QNX ARM based car navigation and it seems this system has a backdoor that enables telnet access without password to the system if a challenge/response succeeds.

When a file called challenge is placed on a USB key and inserted in the system it will write some bytes in it. Here are a few examples: eaxj2ABs4BeMQqQJamOH?smOCVEC KKUcw5m:vvJXmCIK3SBDDqv9p:Or odlwY@ed6B?8OKCmaqIDdFz7YSnv BBqGoWKocmAuvSDacMAkZ:83:QVq

I found the ELF file that handles the challenge/response in the firmware (can share this upon request) and it reads a public key file: hChallengePub = sub_1030A0((int)"/ifs/challenge.pub", &v11, &v13)

challenge.pub contains the following bytes:

30 29 03 02 07 00 02 01 0E 02 0F 00 9C 9C A4 5A
FA 1E 2D 32 2A 93 9D 37 41 93 02 0F 00 95 AB 6B
DB 94 29 4D C3 C6 07 3B B7 31 40

Debug text in the ELF points to source file src/pk/ecc/ecc_import.c which leds me to believe it's an ECC public key but it seems to be incomplete (eg no ASN.1 header).

I want to be able to convert this key into pem format so I can run some tests with openssl so I am looking for pointers how to do this.

Ultimately I'd like to see if I can create proper response and get access but maybe this is impossible if it requires private key (which it should if it's any good).

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src/pk/ecc/ecc_import.c strongly suggests that it's using LibTomCrypt: https://github.com/libtom/libtomcrypt/blob/develop/src/pk/ecc/ecc_import.c

The content of challenge.pub appears to be DER-encoded. It can be decoded as follows:

SEQUENCE(4 elem)
    BIT STRING (1 bit) 0
    INTEGER            14
    INTEGER (112 bit)  3176466357047968568460177262985619
    INTEGER (112 bit)  3035660427084515633934604600553792

As can be seen in the ecc_import.c code referenced above, this translates to:

  • key->type = PK_PUBLIC
  • key_size = 14 bytes
  • key->pubkey.x = 3176466357047968568460177262985619
  • key->pubkey.y = 3035660427084515633934604600553792
  • How to verify it with openssl ? openssl ec -noout -text -inform DER -in challenge.pub -pubin fails: read EC key unable to load Key 24340:error:0D0680A8:asn1 encoding routines:ASN1_CHECK_TLEN:wrong tag:tasn_dec.c:1198: 24340:error:0D07803A:asn1 encoding routines:ASN1_ITEM_EX_D2I:nested asn1 error:tasn_dec.c:372:Type=X509_ALGOR 24340:error:0D08303A:asn1 encoding routines:ASN1_TEMPLATE_NOEXP_D2I:nested asn1 error:tasn_dec.c:694:Field=algor, Type=X509_PUBKEY Missing ASN1 ? – Remko Apr 5 '16 at 17:22
  • LibTomCrypt uses a different format than openssl expects. See superuser.com/questions/900918/… for openssl's expected format. – Jason Geffner Apr 5 '16 at 17:49
  • Accepting this answer as it's very helpful (would still like to convert to OpenSSL compatible PEM format but I will research that) – Remko Apr 11 '16 at 7:29

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