ASN1_GENERATE_NCONF(3SSL)

📦

version 4.0.3 · 14 versions

💖 ASN1_GENERATE_NCONF(3SSL) 💖

okay bestie, this is the OpenSSL manual page for ASN1_generate_nconf and ASN1_generate_v3, and it's genuinely such a niche lil bop. we're talking ASN1 string generation, literally the factory that turns cute little strings into the encoding monsters that X.509 lives on. no cap, this one's for the girls who read DER for breakfast 🥐✨

✨ NAME ✨

ASN1_generate_nconf, ASN1_generate_v3 — the ASN1 string generation functions 🦋

🌸 SYNOPSIS 🌸

#include <openssl/asn1.h>

ASN1_TYPE *ASN1_generate_nconf(const char *str, CONF *nconf);
ASN1_TYPE *ASN1_generate_v3(const char *str, X509V3_CTX *cnf);

like, that's the whole vibe. two functions, both handing you back an ASN1_TYPE 💅

💫 DESCRIPTION 💫

so the way that these work is: they generate the ASN1 encoding of a string, and they hand it to you wrapped in an ASN1_TYPE structure. cute, right? 🎀

str is literally the string you want encoded. nconf or cnf carries the optional configuration info — the place where extra strings get read from. nconf will typically come from a config file, whereas cnf comes from an X509V3_CTX structure, which is typically what the X509 v3 certificate extension functions use. and bestie, if you're not using any additional configuration, you can just set cnf or nconf to NULL. no drama 🌈

🧚 GENERATION STRING FORMAT 🧚

so what actually gets encoded? that's decided by the string str plus the configuration info. here's the general shape of the string:

[modifier,]type[:value]

i.e. zero or more comma separated modifiers, then a type, then an optional colon and a value. the formats of type, value and modifier are all explained down below, bestie 👇

🌟 Supported Types 🌟

here's the roster of supported types. case is not significant in the type names — live your truth, BOOL and bool are the same girl. and unless stated otherwise, only the ASCII format is permissible. 💀

BOOLEAN, BOOL — encodes a boolean type. the value string is mandatory and should be TRUE or FALSE. additionally TRUE, true, Y, y, YES, yes, FALSE, false, N, n, NO and no are all acceptable. so many ways to say yass or nah 🙈
NULL — encodes the NULL type, and the value string must not be present. that's it, that's the whole thing, it's giving minimalism 💅
INTEGER, INT — encodes an ASN1 INTEGER type. the value string represents the value of the integer; it can be prefaced by a minus sign, and it's normally interpreted as a decimal value unless the prefix 0x is included. hex girlies rise up 🔥
ENUMERATED, ENUM — encodes the ASN1 ENUMERATED type, and it's otherwise identical to INTEGER. twin behavior fr fr 👑
OBJECT, OID — encodes an ASN1 OBJECT IDENTIFIER. the value string can be a short name, a long name, or numerical format. pick your fighter ✨
UTCTIME, UTC — encodes an ASN1 UTCTime structure. the value should be in the format YYMMDDHHMMSSZ. yes, that exact format, don't freestyle it 🕐
GENERALIZEDTIME, GENTIME — encodes an ASN1 GeneralizedTime structure. the value should be in the format YYYYMMDDHHMMSSZ. one more Y than its sister, iconic ✨
OCTETSTRING, OCT — encodes an ASN1 OCTET STRING. value represents the contents of this structure, and the format strings ASCII and HEX can be used to specify the format of value. 🫶
BITSTRING, BITSTR — encodes an ASN1 BIT STRING. value represents the contents of this structure, and the format strings ASCII, HEX and BITLIST can be used to specify the format of value.

if the format is anything other than BITLIST, the number of unused bits is set to zero. noting that for the record 📝

UNIVERSALSTRING, UNIV, IA5, IA5STRING, UTF8, UTF8String, BMP, BMPSTRING, VISIBLESTRING, VISIBLE, PRINTABLESTRING, PRINTABLE, T61, T61STRING, TELETEXSTRING, GeneralString, NUMERICSTRING, NUMERIC — these encode the corresponding string types. value represents the contents of this structure. the format can be ASCII or UTF8. that's a whole group chat of aliases right there 💖
SEQUENCE, SEQ, SET — formats the result as an ASN1 SEQUENCE or SET type. value should be a section name, and that section will contain the contents. the field names in the section are ignored, and the values are in the generated string format. if value is absent, then an empty SEQUENCE gets encoded. no value, no problem 🌸

💅 Modifiers 💅

modifiers affect the following structure. they're how you add EXPLICIT or IMPLICIT tagging, add wrappers, or change the string format of the final type and value. supported formats, documented below, bestie:

EXPLICIT, EXP — add an explicit tag to the following structure. this string should be followed by a colon and the tag value to use as a decimal value.

by following the number with U, A, P or C, you can use UNIVERSAL, APPLICATION, PRIVATE or CONTEXT SPECIFIC tagging. the default is CONTEXT SPECIFIC. so if you don't say, it's CONTEXT SPECIFIC, mwah 💋

IMPLICIT, IMP — this is the same as EXPLICIT, except IMPLICIT tagging is used instead. same energy, different tag 🎀
OCTWRAP, SEQWRAP, SETWRAP, BITWRAP — the following structure is surrounded by an OCTET STRING, a SEQUENCE, a SET or a BIT STRING respectively. for a BIT STRING, the number of unused bits is set to zero. wrapping it up like a lil gift 🎁
FORMAT — this specifies the format of the ultimate value. it should be followed by a colon and one of the strings ASCII, UTF8, HEX or BITLIST.

if no format specifier is included, then ASCII is used. if UTF8 is specified, then the value string must be a valid UTF8 string. for HEX, the output must be a set of hex digits. BITLIST (which is only valid for a BIT STRING) is a comma separated list of the indices of the set bits, and all other bits are zero. okay so pick your format carefully, this one matters for real ⚠️

🔥 RETURN VALUES 🔥

ASN1_generate_nconf() and ASN1_generate_v3() return the encoded data as an ASN1_TYPE structure — or NULL if an error occurred. sad girl hours if you get the NULL 😭

the error codes that can be obtained by ERR_get_error(3).

🌈 EXAMPLES 🌈

a simple IA5String:

IA5STRING:Hello World

an IA5String explicitly tagged:

EXPLICIT:0,IA5STRING:Hello World

an IA5String explicitly tagged using APPLICATION tagging:

EXPLICIT:0A,IA5STRING:Hello World

a BITSTRING with bits 1 and 5 set and all others zero:

FORMAT:BITLIST,BITSTRING:1,5

a more complex example using a config file to produce a SEQUENCE consisting of a BOOL an OID and a UTF8String:

asn1 = SEQUENCE:seq_section

[seq_section]

field1 = BOOLEAN:TRUE
field2 = OID:commonName
field3 = UTF8:Third field

this example produces an RSAPrivateKey structure, this is the key contained in the file client.pem in all OpenSSL distributions (note: the field names such as 'coeff' are ignored and are present just for clarity):

asn1=SEQUENCE:private_key
[private_key]
version=INTEGER:0

n=INTEGER:0xBB6FE79432CC6EA2D8F970675A5A87BFBE1AFF0BE63E879F2AFFB93644\
D4D2C6D000430DEC66ABF47829E74B8C5108623A1C0EE8BE217B3AD8D36D5EB4FCA1D9

e=INTEGER:0x010001

d=INTEGER:0x6F05EAD2F27FFAEC84BEC360C4B928FD5F3A9865D0FCAAD291E2A52F4A\
F810DC6373278C006A0ABBA27DC8C63BF97F7E666E27C5284D7D3B1FFFE16B7A87B51D

p=INTEGER:0xF3929B9435608F8A22C208D86795271D54EBDFB09DDEF539AB083DA912\
D4BD57

q=INTEGER:0xC50016F89DFF2561347ED1186A46E150E28BF2D0F539A1594BBD7FE467\
46EC4F

exp1=INTEGER:0x9E7D4326C924AFC1DEA40B45650134966D6F9DFA3A7F9D698CD4ABEA\
9C0A39B9

exp2=INTEGER:0xBA84003BB95355AFB7C50DF140C60513D0BA51D637272E355E397779\
E7B2458F

coeff=INTEGER:0x30B9E4F2AFA5AC679F920FC83F1F2DF1BAF1779CF989447FABC2F5\
628657053A

this example is the corresponding public key in a SubjectPublicKeyInfo structure:

# Start with a SEQUENCE
asn1=SEQUENCE:pubkeyinfo

# pubkeyinfo contains an algorithm identifier and the public key wrapped
# in a BIT STRING
[pubkeyinfo]
algorithm=SEQUENCE:rsa_alg
pubkey=BITWRAP,SEQUENCE:rsapubkey

# algorithm ID for RSA is just an OID and a NULL
[rsa_alg]
algorithm=OID:rsaEncryption
parameter=NULL

# Actual public key: modulus and exponent
[rsapubkey]
n=INTEGER:0xBB6FE79432CC6EA2D8F970675A5A87BFBE1AFF0BE63E879F2AFFB93644\
D4D2C6D000430DEC66ABF47829E74B8C5108623A1C0EE8BE217B3AD8D36D5EB4FCA1D9

e=INTEGER:0x010001

🦋 SEE ALSO 🦋

ERR_get_error(3)

that's it, one friend, but she's a good one 🫶

👑 COPYRIGHT 👑

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>.

and that's the page bestie, mwah 💋 this one shipped as OpenSSL version 4.0.3, dated 2026-09-29, and it lives in the 3SSL manual family. go forth and encode responsibly, no cap 🌸✨💖

📦 where this page comes from

ubuntu stonking: libssl-doc 4.0.3-1ubuntu1 · Apache-2.0
💖 girlified by deepseek-ai/DeepSeek-V4.1-Flash on 2026-11-03: a language model's rewrite of the original, under its terms