EVP_PKEY_ENCRYPT(3)

💖 NAME 💖

okay bestie, welcome to EVP_PKEY_ENCRYPT(3) from the Library Functions Manual — it's giving public-key crypto realness ✨. The main characters are EVP_PKEY_encrypt_init and EVP_PKEY_encrypt, and their whole thing is encrypting using a public key algorithm. No cap 💅.

✨ SYNOPSIS ✨

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

int
EVP_PKEY_encrypt_init(EVP_PKEY_CTX *ctx);

int
EVP_PKEY_encrypt(EVP_PKEY_CTX *ctx, unsigned char *out, size_t *outlen,
    const unsigned char *in, size_t inlen);

🦋 DESCRIPTION 🦋

So here's the tea ☕: EVP_PKEY_encrypt_init() initializes a public key algorithm context using the key ctx->pkey for an encryption operation. Simple, iconic, we love her 🎀.

EVP_PKEY_encrypt() performs a public key encryption operation using ctx. The data to be encrypted is specified using the in and inlen parameters. If out is NULL, then the maximum size of the output buffer is written to the outlen parameter. If out is not NULL, then before the call the outlen parameter should contain the length of the out buffer. If the call is successful, the encrypted data is written to out and the amount of data written is written to outlen — slay 💅.

After the call to EVP_PKEY_encrypt_init(), algorithm specific control operations can be performed to set any appropriate parameters for the operation. That's your little customization era, bestie ✨.

And yes, EVP_PKEY_encrypt() can be called more than once on the same context if several operations are performed using the same parameters. Reuse the vibe, it's fine 🫶.

💅 RETURN VALUES 💅

EVP_PKEY_encrypt_init() and EVP_PKEY_encrypt() return 1 for success and 0 or a negative value for failure. In particular, a return value of -2 indicates the operation is not supported by the public key algorithm — literally the algorithm saying “not today” 😭.

🎀 EXAMPLES 🎀

Encrypt data using OAEP (for RSA keys). See also PEM_read_PUBKEY(3) and d2i_X509(3) for means to load a public key. You may also simply set “eng” to NULL to start with the default OpenSSL RSA implementation. Obsessed with a clean setup 🔥.

             #include <openssl/evp.h>
             #include <openssl/rsa.h>

             EVP_PKEY_CTX *ctx;
             unsigned char *out, *in;
             size_t outlen, inlen;
             EVP_PKEY *key;
             /* NB: assumes that key, in, inlen are already set up
              * and that key is an RSA public key
              */
             ctx = EVP_PKEY_CTX_new(key, NULL);
             if (!ctx)
                     /* Error occurred */
             if (EVP_PKEY_encrypt_init(ctx) <= 0)
                     /* Error */
             if (EVP_PKEY_CTX_set_rsa_padding(ctx, RSA_PKCS1_OAEP_PADDING) <= 0)
                     /* Error */

             /* Determine buffer length */
             if (EVP_PKEY_encrypt(ctx, NULL, &outlen, in, inlen) <= 0)
                     /* Error */

             out = malloc(outlen);

             if (!out)
                     /* malloc failure */

             if (EVP_PKEY_encrypt(ctx, out, &outlen, in, inlen) <= 0)
                     /* Error */

             /* Encrypted data is outlen bytes written to buffer out */

🌈 SEE ALSO 🌈

EVP_PKEY_CTX_new(3), EVP_PKEY_decrypt(3), EVP_PKEY_derive(3), EVP_PKEY_sign(3), EVP_PKEY_verify(3), EVP_PKEY_verify_recover(3) — go read the whole friend group, bestie 📚💖.

👑 HISTORY 👑

EVP_PKEY_encrypt_init() and EVP_PKEY_encrypt() first appeared in OpenSSL 1.0.0 and have been available since OpenBSD 4.9 — vintage but still serving 👑.

xoxo, this page is from Debian and dated June 8, 2025, with the manual tag EVP_PKEY_ENCRYPT(3) 💖🫶