Add RSA key importing functionality for OpenSSL private keys

[beamer159]

TomCrypt currently supports importing OpenSSL RSA public keys. However, OpenSSL private keys cannot be imported currently. Adding this feature would expand this library's usability.

[karel-m]

Could you please post a sample key that you cannot import? Or even better an openssl command used for "unimportable" key generation e.g. openssl genrsa ...?

[sjaeckel]

If you're talking about password-protected RSA private keys you're right. If you remove the password from the key you should be able to import it.
But providing am example-key would be best.

[karel-m]

If you generate an RSA key like this:

openssl genrsa -out test_rsa_private.pem 2048
openssl rsa -in test_rsa_private.pem -out test_rsa_private.der -outform der
openssl rsa -in test_rsa_private.pem -out test_rsa_public.der -outform der -pubout

libtomcrypt should be able to load test_rsa_private.der and test_rsa_public.der (if not then it's a bug).

[beamer159]

Here is the OpenSSL private key I am trying to open. It is not password-protected:

https://pastebin.com/nSZM1Gpt

Some things that I noticed:

For public keys, OpenSSL DER-encodes them differently from TomCrypt keys. A TomCrypt public key has the following structure:

SEQUENCE
    INTEGER
    INTEGER

OpenSSL keys have a different structure:

SEQUENCE
    SEQUENCE
        OBJECT IDENTIFIER
        NULL
    BIT STRING
        SEQUENCE
            INTEGER
            INTEGER

In rsa_import.c, I can find the code that converts the OpenSSL public key structure to the TomCrypt public key structure.

OpenSSL private keys are also encoded differently from TomCrypt private keys. Here's a TomCrypt private key structure:

SEQUENCE
    INTEGER
    INTEGER
    INTEGER
    INTEGER
    INTEGER
    INTEGER
    INTEGER
    INTEGER
    INTEGER

And here's an OpenSSL private key structure:

SEQUENCE
    INTEGER
    SEQUENCE
        OBJECT IDENTIFIER
        NULL
    BIT STRING
        SEQUENCE
            INTEGER
            INTEGER
            INTEGER
            INTEGER
            INTEGER
            INTEGER
            INTEGER
            INTEGER
            INTEGER

However, I don't see any code in rsa_import.c to convert this OpenSSL structure to a TomCrypt structure. It looks like rsa_import.c first tries to decode the key like an OpenSSL public key, then tries to decode the key like a TomCrypt public key, and finally tries to decode the like like a TomCrypt private key.

[karel-m]

Your keys has PKCS#8 format.

The function rsa_import_pkcs8 from #157 is able to load it.

[beamer159]

That function is only provided in dev, correct? Not in the latest release, 1.17?

[karel-m]

Unfortunately it is not even in develop it's currently a pull request.

Just take this file https://github.com/libtom/libtomcrypt/blob/fbcad861e47bd5e9fae047f1da0553adb352abdd/src/pk/rsa/rsa_import_pkcs8.c

[beamer159]

Thank you, I may have gotten that code working a bit, it's very helpful.

I have a question about some parts. The code has rsaoid which is an oid_st datatype. The code also uses corresponding functions pk_get_oid(...). This datatype and function are not in the latest release, 1.17. It looks like this variable is only used to compare with something else. What would be the consequences of removing this check from my implementation?

[beamer159]

Is there any similar code to convert OpenSSL ECC private and public keys to be TomCrypt compliant?

[sjaeckel]

Is there any similar code to convert OpenSSL ECC private and public keys to be TomCrypt compliant?

PR #65 has that, but it's also not merged yet as it's dependant on #187 which isn't merged yet

[sjaeckel]

I'm closing this one as it's a duplicate of #157