OSSL_ENCODER_TO_BIO(3SSL)

💖 OSSL_ENCODER_TO_BIO(3SSL) 💖

okay bestie, so this is the 3SSL manual page for the OpenSSL encoder output squad — the three little functions that actually make your encoding happen and push the bytes somewhere. Sit down, hydrate, let's go 🫶

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✨ NAME ✨

OSSL_ENCODER_to_data, OSSL_ENCODER_to_bio, OSSL_ENCODER_to_fp — Routines to perform an encoding. That's it, that's the whole vibe. 💅

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🎀 SYNOPSIS 🎀

#include <openssl/encoder.h>

int OSSL_ENCODER_to_data(OSSL_ENCODER_CTX *ctx, unsigned char **pdata,
                         size_t *pdata_len);
int OSSL_ENCODER_to_bio(OSSL_ENCODER_CTX *ctx, BIO *out);
int OSSL_ENCODER_to_fp(OSSL_ENCODER_CTX *ctx, FILE *fp);

Feature availability macros, because apparently we gatekeep:

• OSSL_ENCODER_to_fp() is only available when OPENSSL_NO_STDIO is undefined. No STDIO, no fp, no exceptions, that's the rule. 🙈

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🌸 DESCRIPTION 🌸

Let's break it down one icon at a time.

OSSL_ENCODER_to_data() runs the whole encoding process for the context ctx, and the output goes to *pdata and *pdata_len. Two flavours, and the difference is chef's kiss important:

• If *pdata is NULL when you call it, a buffer gets allocated using OPENSSL_zalloc(3), and *pdata gets pointed at the start of that shiny new buffer, and *pdata_len gets assigned its length by the time OSSL_ENCODER_to_data() returns. Fresh buffer, fresh start, main character energy.
• If *pdata is non-NULL when you call it, then *pdata_len is assumed to already hold its size. In that case *pdata will be set to point after the encoded bytes, and *pdata_len will get assigned the number of remaining bytes. So it's like, you're appending, bestie.

OSSL_ENCODER_to_bio() runs the encoding process for the context ctx, with the output going to the BIO out. Simple. Iconic. 🦋

OSSL_ENCODER_to_fp() does the exact same thing as OSSL_ENCODER_to_bio(), except the output goes to the FILE fp instead.

⚠️ okay real talk for both OSSL_ENCODER_to_bio() and OSSL_ENCODER_to_fp(): you (the application) are required to set up the BIO or FILE properly. Like, actually properly. For example, have it in text or binary mode as is appropriate for the encoder output type. Don't come crying to the encoder if you skipped this step 🥲

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💜 RETURN VALUES 💜

OSSL_ENCODER_to_bio(), OSSL_ENCODER_to_fp() and OSSL_ENCODER_to_data() all return 1 on success, or 0 on failure. Binary answer, no gray area, love that for us. ✨

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🌈 EXAMPLES 🌈

💅 Example the first: pkey → PKCS#8, PEM format, into a bio

OSSL_ENCODER_CTX *ectx;
const char *format = "PEM";
const char *structure = "PrivateKeyInfo"; /* PKCS#8 structure */
const unsigned char *pass = "my password";

ectx = OSSL_ENCODER_CTX_new_for_pkey(pkey,
                                     OSSL_KEYMGMT_SELECT_KEYPAIR
                                     | OSSL_KEYMGMT_SELECT_DOMAIN_PARAMETERS,
                                     format, structure,
                                     NULL);
if (ectx == NULL) {
    /* error: no suitable potential encoders found */
}
if (pass != NULL)
    OSSL_ENCODER_CTX_set_passphrase(ectx, pass, strlen(pass));
if (OSSL_ENCODER_to_bio(ectx, bio)) {
    /* pkey was successfully encoded into the bio */
} else {
    /* encoding failure */
}
OSSL_ENCODER_CTX_free(ectx);

💅 Example the second: pkey → PKCS#8, DER format, encrypted with AES-256-CBC, into a buffer

OSSL_ENCODER_CTX *ectx;
const char *format = "DER";
const char *structure = "PrivateKeyInfo"; /* PKCS#8 structure */
const unsigned char *pass = "my password";
unsigned char *data = NULL;
size_t datalen;

ectx = OSSL_ENCODER_CTX_new_for_pkey(pkey,
                                     OSSL_KEYMGMT_SELECT_KEYPAIR
                                     | OSSL_KEYMGMT_SELECT_DOMAIN_PARAMETERS,
                                     format, structure,
                                     NULL);
if (ectx == NULL) {
    /* error: no suitable potential encoders found */
}
if (pass != NULL) {
    OSSL_ENCODER_CTX_set_passphrase(ectx, pass, strlen(pass));
    OSSL_ENCODER_CTX_set_cipher(ctx, "AES-256-CBC", NULL);
}
if (OSSL_ENCODER_to_data(ectx, &data, &datalen)) {
    /*
     * pkey was successfully encoded into a newly allocated
     * data buffer
     */
} else {
    /* encoding failure */
}
OSSL_ENCODER_CTX_free(ectx);

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🦋 SEE ALSO 🦋

provider(7), OSSL_ENCODER_CTX(3) — go read these next, iykyk. 📚

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⭐ HISTORY ⭐

The functions described here were added in OpenSSL 3.0. So they're not ancient relics, they're like... grown but still young. 👑

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👑 COPYRIGHT 👑

Copyright 2019-2021 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (the "License"). You may not use this file except in compliance with the License. You can obtain a copy in the file LICENSE in the source distribution or at <https://www.openssl.org/source/license.html>.

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okay that's the whole page bestie, you ate it, go encode something gorgeous 💖✨

signing off from version 4.0.3, dated 2026-09-29 — this was OSSL_ENCODER_TO_BIO(3SSL), mwah 🎀🫶