CODEWITHSUNDEEP
copensslder
fliX
fliX

Reputation: 813

Extract Public Key of a DER encoded Certificate in C

I am getting a DER encoded certificate (after base64 decode) from an ldap search request and need to parse the public key from it. I am pretty sure that its possible with the openssl library. Unfortunately the API documentation is not very well-kept. Is there any example or other library to extract the information?

Upvotes: 2

Views: 4790

Answers (2)

doptimusprime
doptimusprime

Reputation: 9395

Use d2i_X509 to get the certificate in X509 * structure. After that use X509_get_pubkey to get the public key. X509_get_pubkey will give you public key in EVP_PKEY * structure. I hope this must solve your purpose.

If your certificate is in PEM format (Base64 encoded wrapped by "-----BEGIN CERTIFICATE-----") , then you can also use PEM_read_X509 to get X509 * object directly.

Example:

//Get the X509 object.
//Say certificate is encoded in a file
X509 * xcert = PEM_read_X509(fp, NULL, NULL, NULL);

//or assuming DER encoded certificate in buf with length of buffer is buflen.
X509 * xcert = d2i_X509(NULL, buf, buflen);

//Get the public key.
EVP_PKEY * pubkey = X509_get_pubkey(xcert);


//later free this pubkey object when no longer required.
EVP_PKEY_free(pubkey);

Upvotes: 3

Jay
Jay

Reputation: 24895

You can try to use the d2i_X509 API to decode the DER encoded certificate. It gives you an X509 structure from which you should be able to get the public key.

Upvotes: 1

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