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:
B<[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 OBJECTIDENTIFIER, 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
Emcodes an ASN1 OCTETSTRING. value represents the contents
of this structure, the format strings ASCII and HEX can be
used to specify the format of value.
BITSRING, BITSTR
Emcodes an ASN1 BITSTRING. 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 set bits.
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 more complex example using a config file to produce a
SEQUENCE consiting 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):
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.
The error codes that can be obtained by ERR_get_error(3).