D2I_X509_SIG(3) | Library Functions Manual | D2I_X509_SIG(3)

# NAME

`d2i_X509_SIG`, `i2d_X509_SIG`, `d2i_PKCS8_bio`, `i2d_PKCS8_bio`, `d2i_PKCS8_fp`, `i2d_PKCS8_fp` — decode and encode PKCS#7 digest information

# SYNOPSIS

library “libcrypto”
`#include <openssl/x509.h>`

X509_SIG *
`d2i_X509_SIG`(X509_SIG **val_out, const unsigned char **der_in, long length);

int
`i2d_X509_SIG`(X509_SIG *val_in, unsigned char **der_out);

X509_SIG *
`d2i_PKCS8_bio`(BIO *in_bio, X509_SIG **val_out);

int
`i2d_PKCS8_bio`(BIO *out_bio, X509_SIG *val_in);

X509_SIG *
`d2i_PKCS8_fp`(FILE *in_fp, X509_SIG **val_out);

int
`i2d_PKCS8_fp`(FILE *out_fp, X509_SIG *val_in);

# DESCRIPTION

`d2i_X509_SIG`() and `i2d_X509_SIG`() decode and encode an ASN.1 DigestInfo structure defined in RFC 2315 section 9.4 and equivalently in RFC 8017 section 9.2. For details about the semantics, examples, caveats, and bugs, see ASN1_item_d2i(3).

`d2i_PKCS8_bio`() and `d2i_PKCS8_fp`() are similar to `d2i_X509_SIG`() except that they read from a BIO or FILE pointer.

`i2d_PKCS8_bio`() and `i2d_PKCS8_fp`() are similar to `i2d_X509_SIG`() except that they write to a BIO or FILE pointer.

# RETURN VALUES

`d2i_X509_SIG`(), `d2i_PKCS8_bio`(), and `d2i_PKCS8_fp`() return a X509_SIG object or `NULL` if an error occurs.

`i2d_X509_SIG`() returns the number of bytes successfully encoded or a negative value if an error occurs.

`i2d_PKCS8_bio`() and `i2d_PKCS8_fp`() return 1 for success or 0 if an error occurs.

# SEE ALSO

ASN1_item_d2i(3), PKCS7_new(3), RSA_sign(3), X509_SIG_new(3)

# STANDARDS

RFC 2315: PKCS #7: Cryptographic Message Syntax, section 9: Signed-data content type

RFC 8017: PKCS #1: RSA Cryptography Specifications, section 9: Encoding Methods for Signatures

# HISTORY

`d2i_X509_SIG`() and `i2d_X509_SIG`() first appeared in SSLeay 0.5.1 and have been available since OpenBSD 2.4.

`d2i_PKCS8_bio`(), `i2d_PKCS8_bio`(), `d2i_PKCS8_fp`(), and `i2d_PKCS8_fp`() first appeared in OpenSSL 0.9.4 and have been available since OpenBSD 2.6.

# BUGS

`d2i_PKCS8_bio`(), `i2d_PKCS8_bio`(), `d2i_PKCS8_fp`(), and `i2d_PKCS8_fp`() are severely misnamed and should have been called “d2i_X509_SIG_bio” and so on.

Or arguably, the X509_SIG object is misnamed itself, considering that it represents DigestInfo from PKCS#7 and PKCS#1. Then again, calling it “PKCS8” instead clearly isn't an improvement.

Either way, these names just don't fit.

June 8, 2025 | Debian