Selections¶

The following constants can be used for selection:

EVP_PKEY_KEY_PARAMETERS

Only key parameters will be selected.

EVP_PKEY_PUBLIC_KEY

Only public key components will be selected. This includes optional key parameters.

EVP_PKEY_KEYPAIR

Any keypair components will be selected. This includes the private key, public key and key parameters.

Creating an RSA keypair using raw key data¶

 #include <openssl/evp.h>
 /*
  * These are extremely small to make this example simple.  A real
  * and secure application will not use such small numbers.  A real
  * and secure application is expected to use BIGNUMs, and to build
  * this array dynamically.
  */
 unsigned long rsa_n = 0xbc747fc5;
 unsigned long rsa_e = 0x10001;
 unsigned long rsa_d = 0x7b133399;
 OSSL_PARAM params[] = {
     OSSL_PARAM_ulong("n", &rsa_n),
     OSSL_PARAM_ulong("e", &rsa_e),
     OSSL_PARAM_ulong("d", &rsa_d),
     OSSL_PARAM_END
 };
 int main()
 {
     EVP_PKEY_CTX *ctx = EVP_PKEY_CTX_new_from_name(NULL, "RSA", NULL);
     EVP_PKEY *pkey = NULL;
     if (ctx == NULL
         || EVP_PKEY_fromdata_init(ctx) <= 0
         || EVP_PKEY_fromdata(ctx, &pkey, EVP_PKEY_KEYPAIR, params) <= 0)
         exit(1);
     /* Do what you want with |pkey| */
 }

Creating an ECC keypair using raw key data¶

 #include <openssl/evp.h>
 #include <openssl/param_build.h>
 #include <openssl/ec.h>
 /*
  * Fixed data to represent the private and public key.
  */
 const unsigned char priv_data[] = {
     0xb9, 0x2f, 0x3c, 0xe6, 0x2f, 0xfb, 0x45, 0x68,
     0x39, 0x96, 0xf0, 0x2a, 0xaf, 0x6c, 0xda, 0xf2,
     0x89, 0x8a, 0x27, 0xbf, 0x39, 0x9b, 0x7e, 0x54,
     0x21, 0xc2, 0xa1, 0xe5, 0x36, 0x12, 0x48, 0x5d
 };
 /* UNCOMPRESSED FORMAT */
 const unsigned char pub_data[] = {
     POINT_CONVERSION_UNCOMPRESSED,
     0xcf, 0x20, 0xfb, 0x9a, 0x1d, 0x11, 0x6c, 0x5e,
     0x9f, 0xec, 0x38, 0x87, 0x6c, 0x1d, 0x2f, 0x58,
     0x47, 0xab, 0xa3, 0x9b, 0x79, 0x23, 0xe6, 0xeb,
     0x94, 0x6f, 0x97, 0xdb, 0xa3, 0x7d, 0xbd, 0xe5,
     0x26, 0xca, 0x07, 0x17, 0x8d, 0x26, 0x75, 0xff,
     0xcb, 0x8e, 0xb6, 0x84, 0xd0, 0x24, 0x02, 0x25,
     0x8f, 0xb9, 0x33, 0x6e, 0xcf, 0x12, 0x16, 0x2f,
     0x5c, 0xcd, 0x86, 0x71, 0xa8, 0xbf, 0x1a, 0x47
 };
 int main()
 {
     EVP_PKEY_CTX *ctx;
     EVP_PKEY *pkey = NULL;
     BIGNUM *priv;
     OSSL_PARAM_BLD *param_bld;
     OSSL_PARAM *params = NULL;
     int exitcode = 0;
     priv = BN_bin2bn(priv_data, sizeof(priv_data), NULL);
     param_bld = OSSL_PARAM_BLD_new();
     if (priv != NULL && param_bld != NULL
         && OSSL_PARAM_BLD_push_utf8_string(param_bld, "group",
                                            "prime256v1", 0)
         && OSSL_PARAM_BLD_push_BN(param_bld, "priv", priv)
         && OSSL_PARAM_BLD_push_octet_string(param_bld, "pub",
                                             pub_data, sizeof(pub_data)))
         params = OSSL_PARAM_BLD_to_param(param_bld);
     ctx = EVP_PKEY_CTX_new_from_name(NULL, "EC", NULL);
     if (ctx == NULL
         || params == NULL
         || EVP_PKEY_fromdata_init(ctx) <= 0
         || EVP_PKEY_fromdata(ctx, &pkey, EVP_PKEY_KEYPAIR, params) <= 0) {
         exitcode = 1;
     } else {
         /* Do what you want with |pkey| */
     }
     EVP_PKEY_free(pkey);
     EVP_PKEY_CTX_free(ctx);
     OSSL_PARAM_free(params);
     OSSL_PARAM_BLD_free(param_bld);
     BN_free(priv);
     exit(exitcode);
 }

Finding out params for an unknown key type¶

 #include <openssl/evp.h>
 #include <openssl/core.h>
 /* Program expects a key type as first argument */
 int main(int argc, char *argv[])
 {
     EVP_PKEY_CTX *ctx = EVP_PKEY_CTX_new_from_name(NULL, argv[1], NULL);
     const OSSL_PARAM *settable_params = NULL;
     if (ctx == NULL)
        exit(1);
    settable_params = EVP_PKEY_fromdata_settable(ctx, EVP_PKEY_KEYPAIR);
    if (settable_params == NULL)
         exit(1);
     for (; settable_params->key != NULL; settable_params++) {
         const char *datatype = NULL;
         switch (settable_params->data_type) {
         case OSSL_PARAM_INTEGER:
             datatype = "integer";
             break;
         case OSSL_PARAM_UNSIGNED_INTEGER:
             datatype = "unsigned integer";
             break;
         case OSSL_PARAM_UTF8_STRING:
             datatype = "printable string (utf-8 encoding expected)";
             break;
         case OSSL_PARAM_UTF8_PTR:
             datatype = "printable string pointer (utf-8 encoding expected)";
             break;
         case OSSL_PARAM_OCTET_STRING:
             datatype = "octet string";
             break;
         case OSSL_PARAM_OCTET_PTR:
             datatype = "octet string pointer";
             break;
         }
         printf("%s : %s ", settable_params->key, datatype);
         if (settable_params->data_size == 0)
             printf("(unlimited size)\n");
         else
             printf("(maximum size %zu)\n", settable_params->data_size);
     }
 }

The descriptor OSSL_PARAM(3) returned by EVP_PKEY_fromdata_settable() may also be used programmatically, for example with OSSL_PARAM_allocate_from_text(3).