ASN1_GENERATE_NCONF(3SSL) OpenSSL ASN1_GENERATE_NCONF(3SSL)
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>.
3.5.7 2026-06-09 ASN1_GENERATE_NCONF(3SSL)
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