Question

I used openSSL command to create 2 files: 1 for RSA public key & 1 for RSA private key. How do I recover RSA keys using C?

Specifically, I have these functions:

RSA_public_encrypt(read_num, in_buf, out_buf, public_key, RSA_PKCS1_PADDING);
RSA_private_decrypt(read_num, in_buf, out_buf, private_key, RSA_PKCS1_PADDING);

The 4th arguments, public_key and private_key, need to be in RSA type. But what I have are only 2 text files generated by openSSL command:

File 1: 
-----BEGIN RSA PRIVATE KEY-----
MIICXAIBAAKBgQDP78B9GZ9ZFG6OnZ1PU+9BPoyLRuYJr3rSX470XjbJhmlq9DTn
NvG1pxWxrd5tjlmMWD4AkHqD7E87AafvQEiABdUXwf30LatT1w6tlyQWkM/HCN5k
....
npF+nDtKmGteLJVp5x7HHMnZaRbvcV2oUtgdmIMbqVYgbPkwO2tUfUPA6zg1fzhy
nNzQ35e/Hi0fgSHZib0CQEe4e4txXzkezomkWqwuGL8Qqp8iCbBn44mzxXTBvAQl
muFu93C/ULMzRoq4cpPgl3sS0F9s7+zR18SERerFvfc=
-----END RSA PRIVATE KEY-----

File 2:
-----BEGIN PUBLIC KEY-----
MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDP78B9GZ9ZFG6OnZ1PU+9BPoyL
RuYJr3rSX470XjbJhmlq9DTnNvG1pxWxrd5tjlmMWD4AkHqD7E87AafvQEiABdUX
wf30LatT1w6tlyQWkM/HCN5kmK5WzPUYbI1q5xGy7Eox9sJ6cNwMUOT+MSDhErgB
gkgF6uG1yGrxuEVk/QIDAQAB
-----END PUBLIC KEY-----

Now, I read these 2 files to a char[] array. What I have to do next is convert these 2 arrays to 2 RSA keys (public key at client & private_key at server) so that I can use RSA_public_encrypt and RSA_private_decrypt functions.

Thanks.

Answer 1

Take a look at the I/O functions in the OpenSSL crypto library, specifically the PEM functions

RSA *PEM_read_RSAPrivateKey(FILE *fp, RSA **x,
                                    pem_password_cb *cb, void *u);

RSA *PEM_read_RSAPublicKey(FILE *fp, RSA **x,
                                    pem_password_cb *cb, void *u);

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