EVP_PKEY_NEW(3)

📦 version 4.4.0, in alpine 3.24, arch rolling

🌸 NAME 🌸

hey bestie, welcome to EVP_PKEY_NEW(3) from the Library Functions Manual — we're talking public and private key allocation plus raw key handling, and it's lowkey iconic. The whole squad is: EVP_PKEY_new, EVP_PKEY_up_ref, EVP_PKEY_free, EVP_PKEY_new_raw_private_key, EVP_PKEY_new_raw_public_key, EVP_PKEY_new_mac_key, EVP_PKEY_get_raw_private_key, and EVP_PKEY_get_raw_public_key — literally public and private key allocation and raw key handling functions.

✨ SYNOPSIS ✨

library “libcrypto” #include <openssl/evp.h>

EVP_PKEY *
EVP_PKEY_new(void);

int
EVP_PKEY_up_ref(EVP_PKEY *pkey);

void
EVP_PKEY_free(EVP_PKEY *pkey);

EVP_PKEY *
EVP_PKEY_new_raw_private_key(int type, ENGINE *engine,
    const unsigned char *rawpriv, size_t rawlen);

EVP_PKEY *
EVP_PKEY_new_raw_public_key(int type, ENGINE *engine,
    const unsigned char *rawpub, size_t rawlen);

EVP_PKEY *
EVP_PKEY_new_mac_key(int type, ENGINE *engine,
    const unsigned char *rawpriv, int rawlen);

int
EVP_PKEY_get_raw_private_key(const EVP_PKEY *pkey,
    unsigned char *rawpriv, size_t *rawlen);

int
EVP_PKEY_get_raw_public_key(const EVP_PKEY *pkey, unsigned char *rawpub,
    size_t *rawlen);

🦋 DESCRIPTION 🦋

okay so the EVP_PKEY structure is used by various OpenSSL functions that need a general private or public key without referencing any particular algorithm. it's giving "one key type to rule them all" energy.

  • EVP_PKEY_new() allocates an empty EVP_PKEY structure. The reference count is set to 1. To add a private or public key to it, use the functions described in EVP_PKEY_set1_RSA(3).
  • EVP_PKEY_up_ref() increments the reference count of pkey by 1.
  • EVP_PKEY_free() decrements the reference count of pkey by 1, and if the reference count reaches zero, frees it up. If pkey is a NULL pointer, no action occurs.
  • EVP_PKEY_new_raw_private_key() allocates a new EVP_PKEY. The NID of a public key algorithm that supports raw private keys — i.e. EVP_PKEY_HMAC, EVP_PKEY_X25519, or EVP_PKEY_ED25519 — is provided in the type argument, and rawlen bytes of raw private key data of that type go in rawpriv. The public key data is automatically derived from the given private key data, if appropriate for the algorithm type. The ENGINE *engine argument is always ignored and passing NULL is recommended.
  • EVP_PKEY_new_raw_public_key() works in the same way as EVP_PKEY_new_raw_private_key() except that rawpub points to the raw public key data. The EVP_PKEY structure is initialised without any private key information. Algorithm types that support raw public keys are EVP_PKEY_X25519 and EVP_PKEY_ED25519.
  • EVP_PKEY_new_mac_key() is a deprecated function that achieves the same effect as EVP_PKEY_new_raw_private_key() in a more complicated way and only works with a type of EVP_PKEY_HMAC.
⚠️ bestie, did you catch that? EVP_PKEY_new_mac_key() is deprecated. it's the complicated older sibling, and it only works with EVP_PKEY_HMAC.
  • EVP_PKEY_get_raw_private_key() writes up to *rawlen bytes of raw private key data to the buffer starting at rawpriv and stores the number of bytes written in *rawlen. The calling application is responsible for ensuring that the buffer is large enough to receive the private key data. If the rawpriv argument is NULL, the number of bytes required to hold the key is stored in *rawlen. This function only works for algorithms that support raw private keys. Currently these are EVP_PKEY_HMAC, EVP_PKEY_X25519, and EVP_PKEY_ED25519.
  • EVP_PKEY_get_raw_public_key() is similar to EVP_PKEY_get_raw_private_key() except that it writes raw public key data. This function only works for algorithms that support raw public keys. Currently these are EVP_PKEY_X25519 and EVP_PKEY_ED25519.

🎀 RETURN VALUES 🎀

  • EVP_PKEY_new(), EVP_PKEY_new_raw_private_key(), EVP_PKEY_new_raw_public_key(), and EVP_PKEY_new_mac_key() return either the newly allocated EVP_PKEY structure or NULL if an error occurred.
  • EVP_PKEY_up_ref(), EVP_PKEY_get_raw_private_key(), and EVP_PKEY_get_raw_public_key() return 1 for success or 0 for failure.

🌈 EXAMPLES 🌈

The following code digests a message with HMAC-SHA256:

/* Bogus key: would normally be set from another source */
const unsigned char *key = "key";
const size_t key_len = strlen(key);

const char *msg = "The quick brown fox jumps over the lazy dog";
const size_t msg_len = strlen(msg);

unsigned char *out_mac;
size_t out_len, i;

EVP_PKEY *pkey;
EVP_MD_CTX *md_ctx;

pkey = EVP_PKEY_new_raw_private_key(EVP_PKEY_HMAC, NULL,
    key, key_len);
if (pkey == NULL)
        err(1, "EVP_PKEY_new_raw_private_key");

md_ctx = EVP_MD_CTX_new();
if (md_ctx == NULL)
        err(1, "EVP_MD_CTX_new");

if (EVP_DigestSignInit(md_ctx, NULL, EVP_sha256(), NULL, pkey) == 0)
        err(1, "EVP_DigestSignInit");
if (EVP_DigestSign(md_ctx, NULL, &out_len, msg, msg_len) == 0)
        err(1, "EVP_DigestSign(NULL)");
if ((out_mac = calloc(1, out_len)) == NULL)
        err(1, "calloc");
if (EVP_DigestSign(md_ctx, out_mac, &out_len, msg, msg_len) == 0)
        err(1, "EVP_DigestSign(MAC)");

EVP_MD_CTX_free(md_ctx);
EVP_PKEY_free(pkey);

printf(" MAC = ");
for (i = 0; i < out_len; i++)
        printf("%02x", out_mac[i]);
printf("\n");
free(out_mac);

Even though the type name EVP_PKEY was originally intended to stand for “private key” and the EVP_DigestSignInit(3) API was designed for digital signatures in the context of public key cryptography, both are also used here because a MAC also requires a key, even though that is a symmetric key.

The same code can be used for signing with Ed25519 by making the key ED25519_PRIVATE_KEY_LENGTH = 32 bytes long, replacing EVP_PKEY_HMAC with EVP_PKEY_ED25519, and replacing the call to EVP_sha256(3) with NULL.

💜 SEE ALSO 💜

⭐ HISTORY ⭐

  • EVP_PKEY_new() and EVP_PKEY_free() first appeared in SSLeay 0.6.0 and have been available since OpenBSD 2.4.
  • EVP_PKEY_new_mac_key() first appeared in OpenSSL 1.0.0 and has been available since OpenBSD 4.9.
  • EVP_PKEY_up_ref() first appeared in OpenSSL 1.1.0 and has been available since OpenBSD 6.3.
  • EVP_PKEY_new_raw_private_key(), EVP_PKEY_new_raw_public_key(), EVP_PKEY_get_raw_private_key(), and EVP_PKEY_get_raw_public_key() first appeared in OpenSSL 1.1.1 and have been available since OpenBSD 7.3.

kisses from Debian, June 8, 2025 — this was EVP_PKEY_NEW(3), and she ate. 💖✨

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