Might I suggest reading the documentation? RSA_get0_n() is the function you are wanting.
Pauli -- Dr Paul Dale | Distinguished Architect | Cryptographic Foundations Phone +61 7 3031 7217 Oracle Australia > On 6 May 2020, at 2:20 pm, Thomas Dwyer III <tom...@tomiii.com> wrote: > > I'm porting some old legacy code from OpenSSL 1.0.2 to OpenSSL 3.0.0. A > portion of this code reads X509 certificates, extracts the public key, and > passes it to firmware that I cannot modify. Unfortunately, this legacy > firmware API was very poorly designed such that the public key is passed in a > way similar to: > > RSA *rsa = get_pubkey_from_cert(...) > BIGNUM *bn = rsa->n; > int len = BN_num_bytes(bn); > unsigned char *buf = malloc(len); > BN_bn2bin(bn, buf); > pubkey_to_firmware(buf, len); > > Yuck. Ignoring the fact that this firmware appears to assume a constant > exponent 'e', I cannot find a way to extract the modulus 'n' from the RSA > key. I understand this is intentional. The only solution I could find is to > print the key to a buffer via EVP_PKEY_print_public(), parse the result to > extract the modulus into a giant hex string, and then BN_hex2bn() that back > into a BIGNUM. Is there a better way? > > > Thanks, > Tom.III >
