D2I_RSAPRIVATEKEY(3ossl)

📦
version 15.1 · 2 versions
, in freebsd 15.1

💅 d2i_RSAPRIVATEKEY(3ossl) — the OpenSSL key encode/decode page, explained 🎀

okay bestie, welcome to the d2i_RSAPRIVATEKEY(3ossl) page ✨ — and listen, the headline is kinda major: everything here is DEPRECATED. Not in a cute vintage way. In a "please use the new APIs" way. But you still gotta know what it does, so let's go 💖

🌸 NAME 🌸

A whole squad of old key encode/decode functions, and every single one of them is marked DEPRECATED:

  • DSA decode: d2i_DSAPrivateKey, d2i_DSAPrivateKey_bio, d2i_DSAPrivateKey_fp, d2i_DSAPublicKey, d2i_DSA_PUBKEY, d2i_DSA_PUBKEY_bio, d2i_DSA_PUBKEY_fp, d2i_DSAparams
  • RSA decode: d2i_RSAPrivateKey, d2i_RSAPrivateKey_bio, d2i_RSAPrivateKey_fp, d2i_RSAPublicKey, d2i_RSAPublicKey_bio, d2i_RSAPublicKey_fp, d2i_RSA_PUBKEY, d2i_RSA_PUBKEY_bio, d2i_RSA_PUBKEY_fp
  • DH decode: d2i_DHparams, d2i_DHparams_bio, d2i_DHparams_fp
  • EC decode: d2i_ECParameters, d2i_ECPrivateKey, d2i_ECPrivateKey_bio, d2i_ECPrivateKey_fp, d2i_EC_PUBKEY, d2i_EC_PUBKEY_bio, d2i_EC_PUBKEY_fp
  • RSA encode: i2d_RSAPrivateKey, i2d_RSAPrivateKey_bio, i2d_RSAPrivateKey_fp, i2d_RSAPublicKey, i2d_RSAPublicKey_bio, i2d_RSAPublicKey_fp, i2d_RSA_PUBKEY, i2d_RSA_PUBKEY_bio, i2d_RSA_PUBKEY_fp
  • DH encode: i2d_DHparams, i2d_DHparams_bio, i2d_DHparams_fp
  • DSA encode: i2d_DSAPrivateKey, i2d_DSAPrivateKey_bio, i2d_DSAPrivateKey_fp, i2d_DSAPublicKey, i2d_DSA_PUBKEY, i2d_DSA_PUBKEY_bio, i2d_DSA_PUBKEY_fp, i2d_DSAparams
  • EC encode: i2d_ECParameters, i2d_ECPrivateKey, i2d_ECPrivateKey_bio, i2d_ECPrivateKey_fp, i2d_EC_PUBKEY, i2d_EC_PUBKEY_bio, i2d_EC_PUBKEY_fp

✨ SYNOPSIS ✨

The following functions have been deprecated since OpenSSL 3.0, and can be hidden entirely by defining OPENSSL_API_COMPAT with a suitable version value, see openssl_user_macros(7):

TYPE *d2i_TYPEPrivateKey(TYPE **a, const unsigned char **ppin, long length);
TYPE *d2i_TYPEPrivateKey_bio(BIO *bp, TYPE **a);
TYPE *d2i_TYPEPrivateKey_fp(FILE *fp, TYPE **a);
TYPE *d2i_TYPEPublicKey(TYPE **a, const unsigned char **ppin, long length);
TYPE *d2i_TYPEPublicKey_bio(BIO *bp, TYPE **a);
TYPE *d2i_TYPEPublicKey_fp(FILE *fp, TYPE **a);
TYPE *d2i_TYPEparams(TYPE **a, const unsigned char **ppin, long length);
TYPE *d2i_TYPEparams_bio(BIO *bp, TYPE **a);
TYPE *d2i_TYPEparams_fp(FILE *fp, TYPE **a);
TYPE *d2i_TYPE_PUBKEY(TYPE **a, const unsigned char **ppin, long length);
TYPE *d2i_TYPE_PUBKEY_bio(BIO *bp, TYPE **a);
TYPE *d2i_TYPE_PUBKEY_fp(FILE *fp, TYPE **a);

int i2d_TYPEPrivateKey(const TYPE *a, unsigned char **ppout);
int i2d_TYPEPrivateKey(TYPE *a, unsigned char **ppout);
int i2d_TYPEPrivateKey_fp(FILE *fp, const TYPE *a);
int i2d_TYPEPrivateKey_fp(FILE *fp, TYPE *a);
int i2d_TYPEPrivateKey_bio(BIO *bp, const TYPE *a);
int i2d_TYPEPrivateKey_bio(BIO *bp, TYPE *a);
int i2d_TYPEPublicKey(const TYPE *a, unsigned char **ppout);
int i2d_TYPEPublicKey(TYPE *a, unsigned char **ppout);
int i2d_TYPEPublicKey_fp(FILE *fp, const TYPE *a);
int i2d_TYPEPublicKey_fp(FILE *fp, TYPE *a);
int i2d_TYPEPublicKey_bio(BIO *bp, const TYPE *a);
int i2d_TYPEPublicKey_bio(BIO *bp, TYPE *a);
int i2d_TYPEparams(const TYPE *a, unsigned char **ppout);
int i2d_TYPEparams(TYPE *a, unsigned char **ppout);
int i2d_TYPEparams_fp(FILE *fp, const TYPE *a);
int i2d_TYPEparams_fp(FILE *fp, TYPE *a);
int i2d_TYPEparams_bio(BIO *bp, const TYPE *a);
int i2d_TYPEparams_bio(BIO *bp, TYPE *a);
int i2d_TYPE_PUBKEY(const TYPE *a, unsigned char **ppout);
int i2d_TYPE_PUBKEY(TYPE *a, unsigned char **ppout);
int i2d_TYPE_PUBKEY_fp(FILE *fp, const TYPE *a);
int i2d_TYPE_PUBKEY_fp(FILE *fp, TYPE *a);
int i2d_TYPE_PUBKEY_bio(BIO *bp, const TYPE *a);
int i2d_TYPE_PUBKEY_bio(BIO *bp, TYPE *a);

🦋 DESCRIPTION 🦋

Okay so all functions described here are deprecated. Like, every last one. The glow-up is: use OSSL_DECODER(3) instead of the d2i functions, and OSSL_ENCODER(3) instead of the i2d functions. There's a whole Migration section below, don't worry 💖

In the description here, TYPE is used a placeholder for any of the OpenSSL datatypes, such as RSA. The function parameters ppin and ppout are generally either both named pp in the headers, or in and out.

All the functions here behave the way that's described in d2i_X509(3).

Please note that not all functions in the synopsis are available for all key types. For example, there are no d2i_RSAparams() or i2d_RSAparams(), because the PKCS#1 RSA structure doesn't include any key parameters.

  • d2i_TYPEPrivateKey() and derivates thereof decode DER encoded TYPE private key data organized in a type specific structure.
  • d2i_TYPEPublicKey() and derivates thereof decode DER encoded TYPE public key data organized in a type specific structure.
  • d2i_TYPEparams() and derivates thereof decode DER encoded TYPE key parameters organized in a type specific structure.
  • d2i_TYPE_PUBKEY() and derivates thereof decode DER encoded TYPE public key data organized in a SubjectPublicKeyInfo structure.
  • i2d_TYPEPrivateKey() and derivates thereof encode the private key TYPE data into a type specific DER encoded structure.
  • i2d_TYPEPublicKey() and derivates thereof encode the public key TYPE data into a type specific DER encoded structure.
  • i2d_TYPEparams() and derivates thereof encode the TYPE key parameters data into a type specific DER encoded structure.
  • i2d_TYPE_PUBKEY() and derivates thereof encode the public key TYPE data into a DER encoded SubjectPublicKeyInfo structure.

For example, d2i_RSAPrivateKey() and d2i_RSAPublicKey() expects the structure defined by PKCS#1. Similarly, i2d_RSAPrivateKey() and i2d_RSAPublicKey() produce DER encoded string organized according to PKCS#1.

🌈 Migration 🌈

Migration from the diverse TYPEs requires using corresponding new OpenSSL types. For all TYPEs described here, the corresponding new type is EVP_PKEY. The rest of this section assumes that this has been done, exactly how to do that is described elsewhere.

There are two migration paths:

🧚 Migrating i2d functions to OSSL_ENCODER 🧚

The exact OSSL_ENCODER(3) output is driven by arguments rather than by function names. The sample code to get DER encoded output in a type specific structure is uniform, the only things that vary are the selection of what part of the EVP_PKEY should be output, and the structure. The i2d functions names can therefore be translated into two variables, selection and structure as follows:

i2d_TYPEPrivateKey() translates into:

int selection = EVP_PKEY_KEYPAIR;
const char *structure = "type-specific";

i2d_TYPEPublicKey() translates into:

int selection = EVP_PKEY_PUBLIC_KEY;
const char *structure = "type-specific";

i2d_TYPEparams() translates into:

int selection = EVP_PKEY_PARAMETERS;
const char *structure = "type-specific";

i2d_TYPE_PUBKEY() translates into:

int selection = EVP_PKEY_PUBLIC_KEY;
const char *structure = "SubjectPublicKeyInfo";

The following sample code does the rest of the work:

unsigned char *p = buffer;     /* |buffer| is supplied by the caller */
size_t len = buffer_size;      /* assumed be the size of |buffer| */
OSSL_ENCODER_CTX *ctx =
    OSSL_ENCODER_CTX_new_for_pkey(pkey, selection, "DER", structure,
                                  NULL, NULL);
if (ctx == NULL) {
    /* fatal error handling */
}
if (OSSL_ENCODER_CTX_get_num_encoders(ctx) == 0) {
    OSSL_ENCODER_CTX_free(ctx);
    /* non-fatal error handling */
}
if (!OSSL_ENCODER_to_data(ctx, &p, &len)) {
    OSSL_ENCODER_CTX_free(ctx);
    /* error handling */
}
OSSL_ENCODER_CTX_free(ctx);

💜 NOTES 💜

The letters i and d in i2d_TYPE() stand for "internal" (that is, an internal C structure) and "DER" respectively. So i2d_TYPE() converts from internal to DER.

The functions can also understand BER forms.

The actual TYPE structure passed to i2d_TYPE() must be a valid populated TYPE structure — it cannot simply be fed with an empty structure such as that returned by TYPE_new().

⚠️ The encoded data is in binary form and may contain embedded zeros. Therefore, any FILE pointers or BIOs should be opened in binary mode. Functions such as strlen() will not return the correct length of the encoded structure.

The ways that *ppin and *ppout are incremented after the operation can trap the unwary. See the WARNINGS section in d2i_X509(3) for some common errors. The reason for this-auto increment behaviour is to reflect a typical usage of ASN1 functions: after one structure is encoded or decoded another will be processed after it.

The following points about the data types might be useful:

  • DSA_PUBKEY — Represents a DSA public key using a SubjectPublicKeyInfo structure.
  • DSAPublicKey, DSAPrivateKey — Use a non-standard OpenSSL format and should be avoided; use DSA_PUBKEY, PEM_write_PrivateKey(3), or similar instead.

🫶 RETURN VALUES 🫶

d2i_TYPE(), d2i_TYPE_bio() and d2i_TYPE_fp() return a valid TYPE structure or NULL if an error occurs. If the "reuse" capability has been used with a valid structure being passed in via a, then the object is freed in the event of error and *a is set to NULL.

i2d_TYPE() returns the number of bytes successfully encoded or a negative value if an error occurs.

i2d_TYPE_bio() and i2d_TYPE_fp() return 1 for success and 0 if an error occurs.

🎀 SEE ALSO 🎀

OSSL_ENCODER(3), OSSL_DECODER(3), d2i_PrivateKey(3), d2i_PublicKey(3), d2i_KeyParams(3), d2i_PUBKEY(3), i2d_PrivateKey(3), i2d_PublicKey(3), i2d_KeyParams(3), i2d_PUBKEY(3)

Copyright 2020-2023 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>.

okay that's the whole page bestie, ily, stay encoded 💖✨ This was OpenSSL 3.5.6, dated 2026-04-07, and yes the manual name is D2I_RSAPRIVATEKEY(3ossl) — periodt 🎀🦋💅

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