On 2021/3/11 上午11:42, Jarkko Sakkinen wrote: > On Thu, Mar 11, 2021 at 10:47:50AM +0800, Jia Zhang wrote: >> >> >> On 2021/3/11 上午5:39, Jarkko Sakkinen wrote: >>> On Wed, Mar 10, 2021 at 08:44:44PM +0800, Jia Zhang wrote: >>>> >>>> >>>> On 2021/3/2 下午9:47, Jarkko Sakkinen wrote: >>>>> On Mon, Mar 01, 2021 at 09:54:37PM -0800, Andy Lutomirski wrote: >>>>>> On Mon, Mar 1, 2021 at 9:06 PM Tianjia Zhang >>>>>> <tianjia.zhang@xxxxxxxxxxxxxxxxx> wrote: >>>>>>> >>>>>>> >>>>>>> >>>>>>> On 3/1/21 5:54 PM, Jarkko Sakkinen wrote: >>>>>>>> On Mon, Mar 01, 2021 at 01:18:36PM +0800, Tianjia Zhang wrote: >>>>>>>>> q2 is not always 384-byte length. Sometimes it only has 383-byte. >>>>>>>> >>>>>>>> What does determine this? >>>>>>>> >>>>>>>>> In this case, the valid portion of q2 is reordered reversely for >>>>>>>>> little endian order, and the remaining portion is filled with zero. >>>>>>>> >>>>>>>> I'm presuming that you want to say "In this case, q2 needs to be reversed because...". >>>>>>>> >>>>>>>> I'm lacking these details: >>>>>>>> >>>>>>>> 1. Why the length of Q2 can vary? >>>>>>>> 2. Why reversing the bytes is the correct measure to counter-measure >>>>>>>> this variation? >>>>>>>> >>>>>>>> /Jarkko >>>>>>>> >>>>>>> >>>>>>> When use openssl to generate a key instead of using the built-in >>>>>>> sign_key.pem, there is a probability that will encounter this problem. >>>>>>> >>>>>>> Here is a problematic key I encountered. The calculated q1 and q2 of >>>>>>> this key are both 383 bytes, If the length is not processed, the >>>>>>> hardware signature will fail. >>>>>> >>>>>> Presumably the issue is that some keys have parameters that have >>>>>> enough leading 0 bits to be effectively shorter. The openssl API >>>>>> (and, sadly, a bunch of the ASN.1 stuff) treats these parameters as >>>>>> variable-size integers. >>>>> >>>>> But the test uses a static key. It used to generate a key on fly but >>>> >>>> IMO even though the test code, it comes from the linux kernel, meaning >>>> that its quality has a certain guarantee and it is a good reference, so >>>> the test code still needs to ensure its correctness. >>> >>> Hmm... what is working incorrectly then? >> >> In current implementation, it is working well, after all the static key >> can derive the full 384-byte length of q1 and q2. As mentioned above, if >> someone refers to the design of signing tool from selftest code, it is >> quite possible that the actual implementation will use dynamical or >> external signing key deriving shorter q1 and/or q2 in length. > > A self-test needs is not meant to be generic to be directly used in 3rd > party code. With the current key there is not issue => there is no issue. Alright. So what we should do is to add a comment to explain why the selfcode does something wrong and essentially it is intended. Jia > >> >> Going back the technical background, I'm not a crypto expert, so I >> choose to check the code, doc and make experiment. >> >> Accorindg to intel sdm vol3 37.14: >> >> ``` >> SIGSTRUCT includes four 3072-bit integers (MODULUS, SIGNATURE, Q1, Q2). >> Each such integer is represented as a byte strings of length 384, with >> the most significant byte at the position “offset + 383”, and the least >> significant byte at position “offset”. >> >> ... >> >> The 3072-bit integers Q1 and Q2 are defined by: >> q1 = floor(Signature^2 / Modulus); >> q2 = floor((Signature^3 - q1 * Signature * Modulus) / Modulus); >> ``` >> >> and the implementation of singing tool from Intel SGX SDK >> (https://github.com/intel/linux-sgx/blob/master/sdk/sign_tool/SignTool/sign_tool.cpp#L381 >> ), the most significant byte shuld be at the position “offset + >> q1/q2_actuall_len”, and the padding portion should be filled with zero, >> and don't involve the order reverse, but the selftest code always does. >> This is the root cause of SGX_INVALID_SIGNATURE. >> >> Just simplily enforce size_q1 and size_q2 to SE_KEY_SIZE, and generate >> randome siging key with `openssl genrsa -3 -out signing_key.pem 3072`, >> the SGX_INVALID_SIGNATURE error will appear up quickly. >> >> Jia >> >>> >>> /Jarkko >>> >> > > /Jarkko >
