---
name: "libressl-ASN1_generate_nconf"
section: "3"
platform: "linux"
package: "libressl"
version: "4.4.0-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/libressl-ASN1_generate_nconf"
---

# libressl-ASN1\_generate\_nconf(3)

ASN.1 generation functions

## NAME

**ASN1\_generate\_nconf**, **ASN1\_generate\_v3** – ASN.1 generation functions

## SYNOPSIS

Crypto Library (libcrypto, -lcrypto)

**#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 ASN.1 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. 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**, **Y**, **y**, **YES**, **yes**, **false**, **N**, **n**, **NO** and **no** are acceptable.

- **NULL**

  Encode the NULL type. The *value* string must not be present.

- **INTEGER**, **INT**

  Encodes an ASN.1 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 ASN.1 ENUMERATED type. It is otherwise identical to **INTEGER**.

- **OBJECT**, **OID**

  Encodes an ASN.1 OBJECT IDENTIFIER. The *value* string can be a short name, a long name, or numerical format.

- **UTCTIME**, **UTC**

  Encodes an ASN.1 UTCTime structure. The value should be in the format *YYMMDDHHMMSSZ*.

- **GENERALIZEDTIME**, **GENTIME**

  Encodes an ASN.1 GeneralizedTime structure. The value should be in the format *YYYYMMDDHHMMSSZ*.

- **OCTETSTRING**, **OCT**

  Encodes an ASN.1 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 ASN.1 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.

-

  **BMPSTRING**, **BMP**, **GeneralString**, **IA5STRING**, **IA5**, **NUMERICSTRING**, **NUMERIC**, **PRINTABLESTRING**, **PRINTABLE**, **T61STRING**, **T61**, **TELETEXSTRING**, **UNIVERSALSTRING**, **UNIV**, **UTF8String**, **UTF8**, **VISIBLESTRING**, **VISIBLE** 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 ASN.1 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:

- **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 UTF-8 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 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 that 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 an ASN.1 *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

ASN1\_TYPE\_get(3), d2i\_ASN1\_TYPE(3), [x509v3.cnf(5)](/x509v3.cnf/5.md)

## HISTORY

**ASN1\_generate\_nconf**() and **ASN1\_generate\_v3**() first appeared in OpenSSL 0.9.8 and have been available since OpenBSD 4.5.