D2I_X509_REQ(3)

👑 D2I_X509_REQ 👑

okay so this is the manual page for the section-3 libcrypto functions you're gonna meet in literally every "certificate signing request" moment of your life, and it's called D2I_X509_REQ(3) 💅. It's all about turning PKCS#10 certification requests into bytes and back again. no cap.

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🎀 NAME 🎀

the whole squad, in alphabetical-ish order:

d2i_X509_REQ, i2d_X509_REQ, d2i_X509_REQ_bio, d2i_X509_REQ_fp, i2d_X509_REQ_bio, i2d_X509_REQ_fp, d2i_X509_REQ_INFO, i2d_X509_REQ_INFO — decode and encode PKCS#10 certification requests ✨

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✨ SYNOPSIS ✨

first things first, she lives in the libcrypto library, so:

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

then the actual function lineup, copied exactly because we do not play with prototypes around here 🫶:

X509_REQ *
d2i_X509_REQ(X509_REQ **val_out, const unsigned char **der_in,
    long length);

int
i2d_X509_REQ(X509_REQ *val_in, unsigned char **der_out);

X509_REQ *
d2i_X509_REQ_bio(BIO *in_bio, X509_REQ **val_out);

X509_REQ *
d2i_X509_REQ_fp(FILE *in_fp, X509_REQ **val_out);

int
i2d_X509_REQ_bio(BIO *out_bio, X509_REQ *val_in);

int
i2d_X509_REQ_fp(FILE *out_fp, X509_REQ *val_in);

X509_REQ_INFO *
d2i_X509_REQ_INFO(X509_REQ_INFO **val_out, const unsigned char **der_in,
    long length);

int
i2d_X509_REQ_INFO(X509_REQ_INFO *val_in, unsigned char **der_out);

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💖 DESCRIPTION 💖

So these functions decode and encode PKCS#10 certification requests, periodt. 🦋 And lowkey important: for the details about the semantics, examples, caveats, and bugs, go read ASN1_item_d2i(3) — she's the main character of this whole genre, iykyk.

• d2i_X509_REQ() and i2d_X509_REQ() — decode and encode an ASN.1 CertificationRequest structure defined in RFC 2986 section 4.2. iconic behavior honestly 🔥
• d2i_X509_REQ_bio(), d2i_X509_REQ_fp(), i2d_X509_REQ_bio(), and i2d_X509_REQ_fp() — basically the same thing except they decode or encode using a BIO or FILE pointer. same energy, different plumbing 💅
• d2i_X509_REQ_INFO() and i2d_X509_REQ_INFO() — decode and encode an ASN.1 CertificationRequestInfo structure defined in RFC 2986 section 4.1. she's the inner part, the little sister, and she's valid 🌸

ok real talk — this page just points you at ASN1_item_d2i(3) for the scary parts. If something goes weird with these, that's where the lore lives, not here, fr fr.

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🦋 RETURN VALUES 🦋

the receipts on what you get back:

• d2i_X509_REQ(), d2i_X509_REQ_bio(), and d2i_X509_REQ_fp() return an X509_REQ object or NULL if an error occurs 😭
• d2i_X509_REQ_INFO() returns an X509_REQ_INFO object or NULL if an error occurs 😭
• i2d_X509_REQ() and i2d_X509_REQ_INFO() return the number of bytes successfully encoded or a negative value if an error occurs 💀 (note the negative, bestie, it's not a 0, don't write your error check wrong)
• i2d_X509_REQ_bio() and i2d_X509_REQ_fp() return 1 for success or 0 if an error occurs 🙈 (yeah, this one's just a humble little boolean, she's different from the others)

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🔥 SEE ALSO 🔥

• ASN1_item_d2i(3) — the big sister page with the actual semantics, examples, caveats, and bugs
• PEM_read_X509_REQ(3) — if you're a PEM girlie instead of a DER girlie
• X509_REQ_new(3) — for when you need a fresh blank one to start with 🫶

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🌈 STANDARDS 🌈

RFC 2986: PKCS #10: Certification Request Syntax Specification — and yes that's the whole entry, she keeps it cute and short 💜

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🧚 HISTORY 🧚

past self, present self, future self:

d2i_X509_REQ(), i2d_X509_REQ(), d2i_X509_REQ_fp(), i2d_X509_REQ_fp(), d2i_X509_REQ_INFO(), and i2d_X509_REQ_INFO() first appeared in SSLeay 0.5.1. ✨

d2i_X509_REQ_bio() and i2d_X509_REQ_bio() first appeared in SSLeay 0.6.0. (they're the young ones, they dropped a whole version later, slay for them) ✨

These functions have been available since OpenBSD 2.4. older than most of us and still serving, tbh 👑

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okay bye and good luck with your certification requests, bestie, go decode something iconic 🎀💖 and remember this page came courtesy of Debian, dated June 8, 2025 — that's the source/version and date sign-off, you're welcome ⭐