OSSL_ENCODER_TO_BIO(3ossl)

💖 OSSL_ENCODER_TO_BIO(3ossl) 💖

okay bestie, so this is a page from the OpenSSL manual, and it's literally all about the glow-up moment where your encoder context finally produces output. Three little functions, one big vibe. Let's go. ✨

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🌸 NAME 🌸

OSSL_ENCODER_to_data, OSSL_ENCODER_to_bio, OSSL_ENCODER_to_fp — the routines that actually perform an encoding. Like, they run the thing. That's the whole job. 💅

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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:

OSSL_ENCODER_to_fp() is only available when OPENSSL_NO_STDIO is undefined. no cap. if that macro is defined, that function simply is not invited to the party 🙈

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🦋 DESCRIPTION 🦋

So OSSL_ENCODER_to_data() runs the encoding process for the context ctx, and the output goes to *pdata and *pdata_len. Here's the tea on how that works:

• If *pdata is NULL when you call OSSL_ENCODER_to_data(), a buffer gets allocated using OPENSSL_zalloc(3), and *pdata is set to point at the start of that buffer. Then *pdata_len gets assigned its length when OSSL_ENCODER_to_data() returns. cute, it made you a buffer 🎀
• If *pdata is non-NULL when you call it, then *pdata_len is assumed to hold its size. In that case *pdata gets set to point <em>after</em> the encoded bytes, and *pdata_len gets assigned the number of remaining bytes. so it writes into your buffer and then shuffles the pointers along, main character behavior honestly

Then OSSL_ENCODER_to_bio() runs the encoding process for the context ctx, with the output going to the BIO out. 🫶

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

okay so for OSSL_ENCODER_to_bio() and OSSL_ENCODER_to_fp(), the application is required to set up the BIO or FILE properly — like, for example, having it in text or binary mode as is appropriate for the encoder output type. don't make it guess, bestie, it will not guess for you 😭

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⭐ RETURN VALUES ⭐

OSSL_ENCODER_to_bio(), OSSL_ENCODER_to_fp() and OSSL_ENCODER_to_data() return 1 on success, or 0 on failure. that's it, that's the whole vibe check. 👑

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🌈 EXAMPLES 🌈

💜 Encoding a pkey as PKCS#8 with PEM format into a bio

ok so first one: to encode a pkey as PKCS#8 with 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);

🧚 Encoding a pkey as PKCS#8 with DER format encrypted with AES-256-CBC into a buffer

and the second one: to encode a pkey as PKCS#8 with 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 those too, they're part of the lore 📚

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💫 HISTORY 💫

The functions described here were added in OpenSSL 3.0. so they're not ancient relics, they're relatively new money. 💅

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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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and that's the whole page, bestie!! 🦋 this was OSSL_ENCODER_TO_BIO(3ossl) from OpenSSL version 3.5.9, dated 2026-09-29. slay, go encode something gorgeous 💖✨