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
wherease 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, 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 preceeded 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.
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.
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
consiting of a BOOL an OID and a UTF8String:
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):
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
RETURN VALUES
ASN1_generate_nconf() and ASN1_generate_v3() return the encoded data
as an ASN1_TYPE structure or
NULL if an error occurred.
