ASN1_generate_nconf(3)

ASN1_generate_nconf(3) | OpenSSL | ASN1_generate_nconf(3)

# NAME

ASN1_generate_nconf, ASN1_generate_v3 - 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);

# DESCRIPTION

These functions generate the ASN1 encoding of a string in an ASN1_TYPE structure.

str contains the string to encode. nconf or cnf contains the optional configuration information where additional strings will be read from. nconf will typically come from a config file whereas cnf is obtained from an X509V3_CTX structure, which will typically be used by X509 v3 certificate extension functions. cnf or nconf can be set to NULL if no additional configuration will be used.

# GENERATION STRING FORMAT

The actual data encoded is determined by the string str and the configuration information. The general format of the string is:

[modifier,]type[:value]

That is zero or more comma separated modifiers followed by a type followed by an optional colon and a value. The formats of type, value and modifier are explained below.

## Supported Types

The supported types are listed below. Case is not significant in the type names. Unless otherwise specified only the ASCII format is permissible.

BOOLEAN, BOOL
  This 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 acceptable.
NULL
  Encode the NULL type, the value string must not be present.
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 is normally interpreted as a decimal value unless the prefix 0x is included.
ENUMERATED, ENUM
  Encodes the ASN1 ENUMERATED type, it is otherwise identical to INTEGER.
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.
OCTETSTRING, OCT
  Encodes an ASN1 OCTET STRING. value represents the contents of this structure, 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, 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.

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.
SEQUENCE, SEQ, SET
  Formats the result as an ASN1 SEQUENCE or SET type. value should be a section name which 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 will be encoded.

## Modifiers

Modifiers affect the following structure, they can be used to add EXPLICIT or IMPLICIT tagging, add wrappers or to change the string format of the final type and value. The supported formats are documented below.

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 UNIVERSAL, APPLICATION, PRIVATE or CONTEXT SPECIFIC tagging can be used, the default is CONTEXT SPECIFIC.

IMPLICIT, IMP
  This is the same as EXPLICIT except IMPLICIT tagging is used instead.
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.
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, all other bits are zero.

# RETURN VALUES

ASN1_generate_nconf() and ASN1_generate_v3() return the encoded data as an ASN1_TYPE structure or NULL if an error occurred.

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)

# COPYRIGHT

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>.

2026-04-07 | 3.5.6