D2I_ECPKPARAMETERS(3)

📦 version 4.4.0, in alpine 3.24, arch rolling

💅 NAME 💅

okay so bestie, this is the manual page for D2I_ECPKPARAMETERS(3), and its whole thing is to decode and encode ASN.1 representations of elliptic curve entities. The full squad is:

  • d2i_ECPKParameters, i2d_ECPKParameters, d2i_ECPKParameters_bio, i2d_ECPKParameters_bio, d2i_ECPKParameters_fp, i2d_ECPKParameters_fp
  • d2i_ECParameters, i2d_ECParameters, ECParameters_dup
  • d2i_ECPrivateKey, i2d_ECPrivateKey, d2i_ECPrivateKey_bio, i2d_ECPrivateKey_bio, d2i_ECPrivateKey_fp, i2d_ECPrivateKey_fp
  • o2i_ECPublicKey, i2o_ECPublicKey
  • ECPKParameters_print, ECPKParameters_print_fp, ECParameters_print, ECParameters_print_fp
  • d2i_EC_PUBKEY, i2d_EC_PUBKEY, d2i_EC_PUBKEY_bio, i2d_EC_PUBKEY_bio, d2i_EC_PUBKEY_fp, i2d_EC_PUBKEY_fp

✨ SYNOPSIS ✨

First up, the vibe is libcrypto and this include:

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

Then here's the whole function lineup, exactly as it lives:

EC_GROUP *
d2i_ECPKParameters(EC_GROUP **val_out, const unsigned char **der_in,
    long length);

int
i2d_ECPKParameters(const EC_GROUP *val_in, unsigned char **der_out);

EC_GROUP *
d2i_ECPKParameters_bio(BIO *in_bio, EC_GROUP **val_out);

int
i2d_ECPKParameters_bio(BIO *out_bio, EC_GROUP *val_in);

EC_GROUP *
d2i_ECPKParameters_fp(FILE *in_fp, EC_GROUP **val_out);

int
i2d_ECPKParameters_fp(FILE *out_fp, EC_GROUP *val_in);

EC_KEY *
d2i_ECParameters(EC_KEY **val_out, const unsigned char **der_in,
    long length);

int
i2d_ECParameters(EC_KEY *val_in, unsigned char **der_out);

EC_KEY *
ECParameters_dup(EC_KEY *val_in);

EC_KEY *
d2i_ECPrivateKey(EC_KEY **val_out, const unsigned char **der_in,
    long length);

int
i2d_ECPrivateKey(EC_KEY *val_in, unsigned char **der_out);

EC_KEY *
d2i_ECPrivateKey_bio(BIO *in_bio, EC_KEY **val_out);

int
i2d_ECPrivateKey_bio(BIO *out_bio, EC_KEY *val_in);

EC_KEY *
d2i_ECPrivateKey_fp(FILE *in_fp, EC_KEY **val_out);

int
i2d_ECPrivateKey_fp(FILE *out_fp, EC_KEY *val_in);

EC_KEY *
o2i_ECPublicKey(EC_KEY **val_out, const unsigned char **der_in,
    long length);

int
i2o_ECPublicKey(const EC_KEY *val_in, unsigned char **der_out);

int
ECPKParameters_print(BIO *out_bio, const EC_GROUP *val_in, int indent);

int
ECPKParameters_print_fp(FILE *out_fp, const EC_GROUP *val_in,
    int indent);

int
ECParameters_print(BIO *out_bio, const EC_KEY *val_in);

int
ECParameters_print_fp(FILE *out_fp, const EC_KEY *val_in);

And over here there's a second include for the pubkey girlies:

#include <openssl/x509.h>

EC_KEY *
d2i_EC_PUBKEY(EC_KEY **val_out, const unsigned char **der_in,
    long length);

int
i2d_EC_PUBKEY(EC_KEY *val_in, unsigned char **der_out);

EC_KEY *
d2i_EC_PUBKEY_bio(BIO *in_bio, EC_KEY **val_out);

int
i2d_EC_PUBKEY_bio(BIO *out_bio, EC_KEY *val_in);

EC_KEY *
d2i_EC_PUBKEY_fp(FILE *in_fp, EC_KEY **val_out);

int
i2d_EC_PUBKEY_fp(FILE *out_fp, EC_KEY *val_in);

🌸 DESCRIPTION 🌸

These functions decode and encode elliptic curve keys and parameters. For the full tea on semantics, examples, caveats, and bugs, see ASN1_item_d2i(3).

  • d2i_ECPKParameters() and i2d_ECPKParameters() decode and encode the parameters of an elliptic curve. d2i_ECPKParameters_bio(), i2d_ECPKParameters_bio(), d2i_ECPKParameters_fp(), and i2d_ECPKParameters_fp() are similar except that they decode or encode using a BIO or FILE pointer. Heads up: these four functions are currently implemented as macros.
  • d2i_ECParameters() does the same parsing as d2i_ECPKParameters() but saves the result in the group field of an EC_KEY structure.
  • i2d_ECParameters() produces the same output as i2d_ECPKParameters() but uses val_in->group for input instead of val_in.
  • ECParameters_dup() allocates and initializes an empty EC_KEY object and copies the EC parameters from val_in to it by calling i2d_ECParameters() and d2i_ECParameters(). If a private or public key or any flags are present in val_in, they are not copied.
  • d2i_ECPrivateKey() and i2d_ECPrivateKey() decode and encode an EC private key using an ASN.1 ECPrivateKey structure defined in RFC 5915 section 3 and used for the privateKey field of the ASN.1 PrivateKeyInfo structure defined in RFC 5208 section 5, see PKCS8_PRIV_KEY_INFO_new(3). d2i_ECPrivateKey_bio(), i2d_ECPrivateKey_bio(), d2i_ECPrivateKey_fp(), and i2d_ECPrivateKey_fp() are similar except that they decode or encode using a BIO or FILE pointer.
  • o2i_ECPublicKey() and i2o_ECPublicKey() decode and encode an EC public key. In contrast to ASN1_item_d2i(3), o2i_ECPublicKey() requires val_out, *val_out, and (*val_out)->group to be non-NULL.
  • ECPKParameters_print() and ECPKParameters_print_fp() print human-readable output of the public parameters of the EC_GROUP to out_bio or out_fp. The output lines are indented by indent spaces.
  • ECParameters_print() and ECParameters_print_fp() print the parameter components of val_in to out_bio or out_fp.
  • d2i_EC_PUBKEY() and i2d_EC_PUBKEY() decode and encode an EC public key using an ASN.1 SubjectPublicKeyInfo structure defined in RFC 5280 section 4.1 and documented in X509_PUBKEY_new(3). d2i_EC_PUBKEY_bio(), i2d_EC_PUBKEY_bio(), d2i_EC_PUBKEY_fp(), and i2d_EC_PUBKEY_fp() are similar except that they decode or encode using a BIO or FILE pointer.

🎀 RETURN VALUES 🎀

  • d2i_ECPKParameters(), d2i_ECPKParameters_bio(), and d2i_ECPKParameters_fp() return a valid EC_GROUP structure or NULL if an error occurs.
  • d2i_ECParameters(), ECParameters_dup(), d2i_ECPrivateKey(), d2i_ECPrivateKey_bio(), d2i_ECPrivateKey_fp(), o2i_ECPublicKey(), d2i_EC_PUBKEY(), d2i_EC_PUBKEY_bio(), and d2i_EC_PUBKEY_fp() return a valid EC_KEY structure or NULL if an error occurs.
  • i2d_ECPKParameters(), i2d_ECParameters(), i2d_ECPrivateKey(), i2o_ECPublicKey(), and i2d_EC_PUBKEY() return the number of bytes successfully encoded or a negative value if an error occurs.
  • i2d_ECPKParameters_bio(), i2d_ECPKParameters_fp(), i2d_ECPrivateKey_bio(), i2d_ECPrivateKey_fp(), ECPKParameters_print(), ECPKParameters_print_fp(), ECParameters_print(), ECParameters_print_fp(), i2d_EC_PUBKEY_bio(), and i2d_EC_PUBKEY_fp() return 1 for success or 0 if an error occurs.

🦋 SEE ALSO 🦋

Go check out these besties:

🌈 STANDARDS 🌈

  • RFC 5915: Elliptic Curve Private Key Structure
  • RFC 5208: Public-Key Cryptography Standards (PKCS) #8: Private-Key Information Syntax Specification
  • RFC 5280: Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile, section 4.1: Basic Certificate Fields

👑 HISTORY 👑

d2i_ECPKParameters(), i2d_ECPKParameters(), d2i_ECPKParameters_bio(), i2d_ECPKParameters_bio(), d2i_ECPKParameters_fP(), i2d_ECPKParameters_fp(), d2i_ECParameters(), i2d_ECParameters(), ECParameters_dup(), d2i_ECPrivateKey(), i2d_ECPrivateKey(), d2i_ECPrivateKey_bio(), i2d_ECPrivateKey_bio(), d2i_ECPrivateKey_fp(), i2d_ECPrivateKey_fp(), o2i_ECPublicKey(), i2o_ECPublicKey(), ECPKParameters_print(), ECPKParameters_print_fp(), ECParameters_print(), ECParameters_print_fp(), d2i_EC_PUBKEY(), i2d_EC_PUBKEY(), d2i_EC_PUBKEY_bio(), i2d_EC_PUBKEY_bio(), d2i_EC_PUBKEY_fp(), and i2d_EC_PUBKEY_fp() first appeared in OpenSSL 0.9.8 and have been available since OpenBSD 4.5.

💖 xoxo, this lil page came from Debian, dated June 8, 2025, and it's the D2I_ECPKPARAMETERS(3) manual — bye bestie! 💖

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