ASN1_GENERATE_NCONF(3ossl)

📦
version 3.5.9 · 8 versions
, in fedora 43, fedora 44

💖 NAME 💖

ASN1_generate_nconf, ASN1_generate_v3 — the ASN1 string generation girlies 💅 (this is the ASN1_GENERATE_NCONF(3ossl) page, bestie, welcome to OpenSSL's manual set 🫶)

🌸 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);

✨ DESCRIPTION ✨

okay so these two functions? they generate the ASN1 encoding of a string, and they hand it back to you inside an ASN1_TYPE structure. iconic behaviour honestly 💜

str is the string you wanna encode. nconf or cnf holds the optional configuration info — that's where any extra strings get read from. nconf is typically coming from a config file, whereas cnf comes from an X509V3_CTX structure, which is what the X509 v3 certificate extension functions usually reach for. and here's the thing: cnf or nconf can be set to NULL if you're not using any additional config at all. no config, no problem 🧚

🦋 GENERATION STRING FORMAT 🦋

so the actual data that gets encoded? it's decided by the string str plus the configuration info. the general format of the string is:

[modifier,]type[:value]

which is literally: zero or more comma separated modifiers, then a type, then an optional colon and a value. and the formats of type, value and modifier are explained below bestie, keep reading ⭐

👑 Supported Types 👑

the supported types are all listed below. case is not significant in the type names. and unless it says otherwise, only the ASCII format is permissible.

  • BOOLEAN, BOOL — encodes a boolean type. the value string is mandatory and should be TRUE or FALSE. also acceptable: TRUE, true, Y, y, YES, yes, FALSE, false, N, n, NO and no. so many ways to say yes or no, we love options 💅
  • NULL — encodes the NULL type. the value string must not be present. not even a little. don't try it 🙈
  • INTEGER, INT — encodes an ASN1 INTEGER type. the value string is 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 🔥
  • ENUMERATED, ENUM — encodes the ASN1 ENUMERATED type. otherwise it's identical to INTEGER. same vibe, different label fr fr
  • OBJECT, OID — encodes an ASN1 OBJECT IDENTIFIER. the value string can be a short name, a long name, or numerical format.
  • UTCTIME, UTC — encodes an ASN1 UTCTime structure. the value should be in the format YYMMDDHHMMSSZ.
  • GENERALIZEDTIME, GENTIME — encodes an ASN1 GeneralizedTime structure. the value should be in the format YYYYMMDDHHMMSSZ. yes it gets the extra Y's, it's the main character of timestamps 👑
  • 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. noted 📝

  • 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. yes that's a lot of names, they're all valid, collect them like stickers 🎀
  • 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. we love a chill optional field 💜

💅 Modifiers 💅

modifiers affect the following structure. you use them to 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 — adds 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.

and if you follow the number with U, A, P or C, then UNIVERSAL, APPLICATION, PRIVATE or CONTEXT SPECIFIC tagging can be used. the default is CONTEXT SPECIFIC. pick your fighter ✨

  • IMPLICIT, IMP — same as EXPLICIT except IMPLICIT tagging is used instead. sibling energy 🫶
  • OCTWRAP, SEQWRAP, SETWRAP, BITWRAP — the following structure gets surrounded by an OCTET STRING, a SEQUENCE, a SET or a BIT STRING respectively. and for a BIT STRING, the number of unused bits is set to zero. wrap it up, gift it, slay 🎁
  • FORMAT — 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. so precise, so demure 💅

💜 RETURN VALUES 💜

ASN1_generate_nconf() and ASN1_generate_v3() return the encoded data as an ASN1_TYPE structure, or NULL if an error occurred. (crying, throwing up, etc 😭)

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 — it's 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. they're decorative bestie, aesthetic only 🎀)

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
heads up bestie: those backslashes at the end of the long hex lines are line continuations, copy them exactly or the whole thing falls apart. no cap 💀

⭐ SEE ALSO ⭐

Copyright 2002-2021 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>.

and that's the whole page, babe 🫶 this was OpenSSL version 3.5.9, dated 2026-09-29, filed under ASN1_GENERATE_NCONF(3ossl). go generate some ASN1, you've got this 💖✨👑

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