> The rsa_mod_exp function is only called for private key operations. You can't > tell if it is a private encrypt or a private decrypt though but that > shouldn't matter because the operation performed at that level is the same for > both.
Ah, I see. So to clarify (pls correct me if I'm wrong): * rsa_mod_exp() is the modular exponentiation function that openSSL will attempt to use for all private key operations (if RSA_FLAG_EXT_PKEY is set, or the private parameters of that method are non-null), before defaulting to bn_mod_exp(). * And bn_mod_exp() is the modular exponentiation function used by all public key operations So in my case, I should set RSA_FLAG_EX_PKEY in my engine's RSA_METHOD struct, and then implement my own versions of rsa_mod_exp (for the private key encryption/decryption), and bn_mod_exp (for the public key encryption/decryption). Brett ________________________________ From: openssl-dev <openssl-dev-boun...@openssl.org> on behalf of Dr. Stephen Henson <st...@openssl.org> Sent: Sunday, August 27, 2017 6:45 PM To: openssl-dev@openssl.org Subject: Re: [openssl-dev] confusion with rsa_meth_st in a custom RSA engine On Sun, Aug 27, 2017, Brett R. Nicholas wrote: > > This makes sense to me, and it seems that is the desired behavior. However, > if I *only* reimplement the rsa_mod_exp() function, and leave the > encrypt/decrypt functions to the default openSSL implementations, how can my > engine know which of the four of those functions called its rsa_mod_exp > function()? To put it another way: my accelerator will need to know whether > it is meant to perform public key or private key operations, since the > inputs will be written to different memory addresses. From within > rsa_mod_exp(), the only way I can think of determining whether the function > has been called by private_encrypt/decrypt() or public_encrypt/decrypt would > be to check if the p and q fields of the RSA *rsa struct passed into the > function are NULL? But I can't tell from the source code if this will be > guaranteed just by having RSA_FLAG_EXT_PKEY set in the "flags" field of my > engine's RSA_METHOD. > The rsa_mod_exp function is only called for private key operations. You can't tell if it is a private encrypt or a private decrypt though but that shouldn't matter because the operation performed at that level is the same for both. Steve. -- Dr Stephen N. Henson. OpenSSL project core developer. Commercial tech support now available see: https://na01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.openssl.org&data=02%7C01%7Cbrett.r.nicholas.th%40dartmouth.edu%7C5374bb23132c4377080c08d4edb671de%7C995b093648d640e5a31ebf689ec9446f%7C0%7C0%7C636394815232517002&sdata=AdSj9Ys%2FG%2FQ1VJIIaD5kZhAwbki5mcF0AL8b2UBxic4%3D&reserved=0 -- openssl-dev mailing list To unsubscribe: https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fmta.openssl.org%2Fmailman%2Flistinfo%2Fopenssl-dev&data=02%7C01%7Cbrett.r.nicholas.th%40dartmouth.edu%7C5374bb23132c4377080c08d4edb671de%7C995b093648d640e5a31ebf689ec9446f%7C0%7C0%7C636394815232517002&sdata=zzQB9AlLiORZC2btJ6zi1MZQxVzoB8pgWHTtAC8LHtM%3D&reserved=0
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