Typos and RSA

I am working on hooking up RSA functionality to the akcipher API. It appears that no other code, to date, uses this API. Can anyone confirm or deny that conclusion?

I have questions about invoking akcipher transform functions, and can find no information about specifics that vex me. If there is other code to look at, I'm happy to. Otherwise, I can embarrass myself here with a display of ignorance.

Gary

Am Dienstag, 17. Mai 2016, 16:22:43 schrieb Gary R Hook:

Hi Gary,

This is not correct. The asymmetric key API uses that code. So does the module signing code.

Ciao
Stephan

Also you can have a look at testmgr.c for examples. "git grep crypto_alloc_akcipher" is also useful.

Thanks,

TS

Thanks so much.

There are exactly 3 references to that symbol (in my freshly pulled copy of cryptodev-2.6). testmgr.c precipitates my questions, and public_key.c doesn't actually provide any content in the source input buffer, neither modulus nor plaintext. Thus, it doesn't clarify things either.

But I truly appreciate your attention.

So I'll go ahead and ask, because I did look at the two areas mentioned by Stephan, but neither seem to clarify (to my admittedly ignorant eyes... I'm a real newbie on crypto here) usage.

Here's my question:

The source input (as set via akcipher_request_set_crypt()) to akcipher is supposed to be the modulus + plaintext. testmgr hands this in via a scatterlist with 2 elements, wherein the first is the modulus, the second the payload. The source length however, appears to be the aggregate length of these two elements. Okay, good enough.

Since the API provides no information about the modulus length, one might guess that the only way to ascertain the separate lengths of the two parts is to read the values from the scatterlist structures. I get that the key (exponent) length is what really matters, but the source input fields are clearly of arbitrary and unequal length.

So please forgive my ignorance, but I'm not seeing it: how do we decompose the two parts of src and get their lengths? What can we expect on the receiving end of the encrypt function with respect to the source data structure? A two-element scatterlist? Or...? What can we conclude from the calls made in do_test_rsa() in testmgr.c, vs the call in public_key_verify_signature() in public_key.c re: invocation and provided data.

Any clarification is greatly appreciated.

Gary

Am Dienstag, 17. Mai 2016, 17:46:44 schrieb Gary R Hook:

Hi Gary,

Here is an example from a current code of mine (all kccavs symbols are private to my code):

        tfm = crypto_alloc_akcipher(kccavs_test->name, 0, 0);
        if (IS_ERR(tfm)) {
                pr_info("could not allocate akcipher handle for %s %ld\n",
                        kccavs_test->name, PTR_ERR(tfm));
                return PTR_ERR(tfm);
        }

        req = akcipher_request_alloc(tfm, GFP_KERNEL);
        if (!req)
                goto err;

        if (crypto_akcipher_maxsize(tfm) > MAXDATALEN) {
                err = -ENOMEM;
                pr_info("output datasize is too big\n");
                goto err;
        }

        err = crypto_akcipher_set_pub_key(tfm, key->data, key->len);
        if (err)
                goto err;

        err = kccavs_akcipher_hashdata();
        if (err)
                goto err;

        rsa.tfm = tfm;
        rsa.req = req;
        init_completion(&rsa.result.completion);

        sg_init_one(&src, rsa_sig->data, rsa_sig->len);
        akcipher_request_set_crypt(req, &src, &src, rsa_sig->len,
                                   crypto_akcipher_maxsize(tfm));

        err = crypto_akcipher_verify(req);
        kccavs_akcipher_wait(&rsa, err);

        dbg("RSA signature verification result %d\n", err);

        rsa_sig->len = min_t(u64, rsa_sig->len, data->len);

        if (!err) {
                /* sig ver passed */
                if (data->len == rsa_sig->len &&
                    !memcmp(rsa_sig->data, data->data, rsa_sig->len)) {
                        dbg("sig ver op passed, good data");
                        memcpy(kccavs_test->data.data, "\xbe\xef\xbe\xef", 4);
                } else {
                        dbg("sig ver op passed, wrong data");
                        memcpy(kccavs_test->data.data, "\xde\xad\xbe\xef", 4);
                }
        } else {
                /*
                 * Signature verify failed
                 * Note, the CAVS vectors may sometimes even provide wrong
                 * input data that do not comply with some requirements. In
                 * this case, the kernel returns errors other than EBADMSG.
                 */
                memcpy(kccavs_test->data.data, "\xde\xad\xbe\xef", 4);
        }

crypto_akcipher_maxsize(tfm)?

Depending on what type of RSA operation you use (raw or pkcs1) or the operation type (siggen/ver), the input is not just the modulus.

So, to help you, you need to give a bit more information about what type of RSA operation you want to perform.

Ciao
Stephan

Ah.... enlightenment can be such an uncomfortable thing...

Yes, thank you. After spending more time wandering through rsa.c & rsa_helper.c I have come to realize that I have been laboring under a paradigm imposed by my implementation requirements. Now that I have that cleared up, the answer to my question it self-evident.Although I'm still not clear on why testmgr feels the need to create a SGL table with an empty second element (for the existing tests), rather than a single SGL. But that's neither here nor there.

As I said, I'm a newbie with lots to learn about this stuff. Thanks for your patience.

Because the role of testmgr is to test different scenarios like more than one entry in an sgl, etc.
Thanks,

TS