openssl/doc/asn1.doc

The ASN.1 Routines.

ASN.1 is a specification for how to encode structured 'data' in binary form.
The approach I have take to the manipulation of structures and their encoding
into ASN.1 is as follows.

For each distinct structure there are 4 function of the following form
TYPE *TYPE_new(void);
void TYPE_free(TYPE *);
TYPE *d2i_TYPE(TYPE **a,unsigned char **pp,long length);
long i2d_TYPE(TYPE *a,unsigned char **pp); 	/* CHECK RETURN VALUE */

where TYPE is the type of the 'object'.  The TYPE that have these functions
can be in one of 2 forms, either the internal C malloc()ed data structure
or in the DER (a variant of ASN.1 encoding) binary encoding which is just
an array of unsigned bytes.  The 'i2d' functions converts from the internal
form to the DER form and the 'd2i' functions convert from the DER form to
the internal form.

The 'new' function returns a malloc()ed version of the structure with all
substructures either created or left as NULL pointers.  For 'optional'
fields, they are normally left as NULL to indicate no value.  For variable
size sub structures (often 'SET OF' or 'SEQUENCE OF' in ASN.1 syntax) the
STACK data type is used to hold the values.  Have a read of stack.doc
and have a look at the relevant header files to see what I mean.  If there
is an error while malloc()ing the structure, NULL is returned.

The 'free' function will free() all the sub components of a particular
structure.  If any of those sub components have been 'removed', replace
them with NULL pointers, the 'free' functions are tolerant of NULL fields.

The 'd2i' function copies a binary representation into a C structure.  It
operates as follows.  'a' is a pointer to a pointer to
the structure to populate, 'pp' is a pointer to a pointer to where the DER
byte string is located and 'length' is the length of the '*pp' data.
If there are no errors, a pointer to the populated structure is returned.
If there is an error, NULL is returned.  Errors can occur because of
malloc() failures but normally they will be due to syntax errors in the DER
encoded data being parsed. It is also an error if there was an
attempt to read more that 'length' bytes from '*p'.  If
everything works correctly, the value in '*p' is updated
to point at the location just beyond where the DER
structure was read from.  In this way, chained calls to 'd2i' type
functions can be made, with the pointer into the 'data' array being
'walked' along the input byte array.
Depending on the value passed for 'a', different things will be done.  If
'a' is NULL, a new structure will be malloc()ed and returned.  If '*a' is
NULL, a new structure will be malloc()ed and put into '*a' and returned.
If '*a' is not NULL, the structure in '*a' will be populated, or in the
case of an error, free()ed and then returned.
Having these semantics means that a structure
can call a 'd2i' function to populate a field and if the field is currently
NULL, the structure will be created.

The 'i2d' function type is used to copy a C structure to a byte array.
The parameter 'a' is the structure to convert and '*p' is where to put it.
As for the 'd2i' type structure, 'p' is updated to point after the last
byte written.  If p is NULL, no data is written.  The function also returns
the number of bytes written.  Where this becomes useful is that if the
function is called with a NULL 'p' value, the length is returned.  This can
then be used to malloc() an array of bytes and then the same function can
be recalled passing the malloced array to be written to. e.g.

int len;
unsigned char *bytes,*p;
len=i2d_X509(x,NULL);	/* get the size of the ASN1 encoding of 'x' */
if ((bytes=(unsigned char *)malloc(len)) == NULL)
	goto err;
p=bytes;
i2d_X509(x,&p);

Please note that a new variable, 'p' was passed to i2d_X509.  After the
call to i2d_X509 p has been incremented by len bytes.

Now the reason for this functional organisation is that it allows nested
structures to be built up by calling these functions as required.  There
are various macros used to help write the general 'i2d', 'd2i', 'new' and
'free' functions.  They are discussed in another file and would only be
used by some-one wanting to add new structures to the library.  As you
might be able to guess, the process of writing ASN.1 files can be a bit CPU
expensive for complex structures.  I'm willing to live with this since the
simpler library code make my life easier and hopefully most programs using
these routines will have their execution profiles dominated by cipher or
message digest routines.
What follows is a list of 'TYPE' values and the corresponding ASN.1
structure and where it is used.

TYPE			ASN.1
ASN1_INTEGER		INTEGER
ASN1_BIT_STRING		BIT STRING
ASN1_OCTET_STRING	OCTET STRING
ASN1_OBJECT		OBJECT IDENTIFIER
ASN1_PRINTABLESTRING	PrintableString
ASN1_T61STRING		T61String
ASN1_IA5STRING		IA5String
ASN1_UTCTIME		UTCTime
ASN1_TYPE		Any of the above mentioned types plus SEQUENCE and SET

Most of the above mentioned types are actualled stored in the
ASN1_BIT_STRING type and macros are used to differentiate between them.
The 3 types used are

typedef struct asn1_object_st
	{
	/* both null if a dynamic ASN1_OBJECT, one is
	 * defined if a 'static' ASN1_OBJECT */
	char *sn,*ln;
	int nid;
	int length;
	unsigned char *data;
	} ASN1_OBJECT;
This is used to store ASN1 OBJECTS.  Read 'objects.doc' for details ono
routines to manipulate this structure.  'sn' and 'ln' are used to hold text
strings that represent the object (short name and long or lower case name).
These are used by the 'OBJ' library.  'nid' is a number used by the OBJ
library to uniquely identify objects.  The ASN1 routines will populate the
'length' and 'data' fields which will contain the bit string representing
the object.

typedef struct asn1_bit_string_st
	{
	int length;
	int type;
	unsigned char *data;
	} ASN1_BIT_STRING;
This structure is used to hold all the other base ASN1 types except for
ASN1_UTCTIME (which is really just a 'char *').  Length is the number of
bytes held in data and type is the ASN1 type of the object (there is a list
in asn1.h).

typedef struct asn1_type_st
	{
	int type;
	union	{
		char *ptr;
		ASN1_INTEGER *		integer;
		ASN1_BIT_STRING *	bit_string;
		ASN1_OCTET_STRING *	octet_string;
		ASN1_OBJECT *		object;
		ASN1_PRINTABLESTRING *	printablestring;
		ASN1_T61STRING *	t61string;
		ASN1_IA5STRING *	ia5string;
		ASN1_UTCTIME *		utctime;
		ASN1_BIT_STRING *	set;
		ASN1_BIT_STRING *	sequence;
		} value;
	} ASN1_TYPE;
This structure is used in a few places when 'any' type of object can be
expected.

X509			Certificate
X509_CINF		CertificateInfo
X509_ALGOR		AlgorithmIdentifier
X509_NAME		Name			
X509_NAME_ENTRY		A single sub component of the name.
X509_VAL		Validity
X509_PUBKEY		SubjectPublicKeyInfo
The above mentioned types are declared in x509.h. They are all quite
straight forward except for the X509_NAME/X509_NAME_ENTRY pair.
A X509_NAME is a STACK (see stack.doc) of X509_NAME_ENTRY's.
typedef struct X509_name_entry_st
	{
	ASN1_OBJECT *object;
	ASN1_BIT_STRING *value;
	int set;
	int size; 	/* temp variable */
	} X509_NAME_ENTRY;
The size is a temporary variable used by i2d_NAME and set is the set number
for the particular NAME_ENTRY.  A X509_NAME is encoded as a sequence of
sequence of sets.  Normally each set contains only a single item.
Sometimes it contains more.  Normally throughout this library there will be
only one item per set.  The set field contains the 'set' that this entry is
a member of.  So if you have just created a X509_NAME structure and
populated it with X509_NAME_ENTRYs, you should then traverse the X509_NAME
(which is just a STACK) and set the 'set/' field to incrementing numbers.
For more details on why this is done, read the ASN.1 spec for Distinguished
Names.

X509_REQ		CertificateRequest
X509_REQ_INFO		CertificateRequestInfo
These are used to hold certificate requests.

X509_CRL		CertificateRevocationList
These are used to hold a certificate revocation list

RSAPrivateKey		PrivateKeyInfo
RSAPublicKey		PublicKeyInfo
Both these 'function groups' operate on 'RSA' structures (see rsa.doc).
The difference is that the RSAPublicKey operations only manipulate the m
and e fields in the RSA structure.

DSAPrivateKey		DSS private key
DSAPublicKey		DSS public key
Both these 'function groups' operate on 'DSS' structures (see dsa.doc).
The difference is that the RSAPublicKey operations only manipulate the 
XXX fields in the DSA structure.

DHparams		DHParameter
This is used to hold the p and g value for The Diffie-Hellman operation.
The function deal with the 'DH' strucure (see dh.doc).

Now all of these function types can be used with several other functions to give
quite useful set of general manipulation routines.  Normally one would
not uses these functions directly but use them via macros. 

char *ASN1_dup(int (*i2d)(),char *(*d2i)(),char *x);
'x' is the input structure case to a 'char *', 'i2d' is the 'i2d_TYPE'
function for the type that 'x' is and d2i is the 'd2i_TYPE' function for the
type that 'x' is.  As is obvious from the parameters, this function
duplicates the strucutre by transforming it into the DER form and then
re-loading it into a new strucutre and returning the new strucutre.  This
is obviously a bit cpu intensive but when faced with a complex dynamic
structure this is the simplest programming approach.  There are macros for
duplicating the major data types but is simple to add extras.

char *ASN1_d2i_fp(char *(*new)(),char *(*d2i)(),FILE *fp,unsigned char **x);
'x' is a pointer to a pointer of the 'desired type'.  new and d2i are the
corresponding 'TYPE_new' and 'd2i_TYPE' functions for the type and 'fp' is
an open file pointer to read from.  This function reads from 'fp' as much
data as it can and then uses 'd2i' to parse the bytes to load and return
the parsed strucutre in 'x' (if it was non-NULL) and to actually return the
strucutre.  The behavior of 'x' is as per all the other d2i functions.

char *ASN1_d2i_bio(char *(*new)(),char *(*d2i)(),BIO *fp,unsigned char **x);
The 'BIO' is the new IO type being used in SSLeay (see bio.doc).  This
function is the same as ASN1_d2i_fp() except for the BIO argument.
ASN1_d2i_fp() actually calls this function.

int ASN1_i2d_fp(int (*i2d)(),FILE *out,unsigned char *x);
'x' is converted to bytes by 'i2d' and then written to 'out'.  ASN1_i2d_fp
and ASN1_d2i_fp are not really symetric since ASN1_i2d_fp will read all
available data from the file pointer before parsing a single item while
ASN1_i2d_fp can be used to write a sequence of data objects.  To read a
series of objects from a file I would sugest loading the file into a buffer
and calling the relevent 'd2i' functions.

char *ASN1_d2i_bio(char *(*new)(),char *(*d2i)(),BIO *fp,unsigned char **x);
This function is the same as ASN1_i2d_fp() except for the BIO argument.
ASN1_i2d_fp() actually calls this function.

char *	PEM_ASN1_read(char *(*d2i)(),char *name,FILE *fp,char **x,int (*cb)());
This function will read the next PEM encoded (base64) object of the same
type as 'x' (loaded by the d2i function).  'name' is the name that is in
the '-----BEGIN name-----' that designates the start of that object type.
If the data is encrypted, 'cb' will be called to prompt for a password.  If
it is NULL a default function will be used to prompt from the password.
'x' is delt with as per the standard 'd2i' function interface.  This
function can be used to read a series of objects from a file.  While any
data type can be encrypted (see PEM_ASN1_write) only RSA private keys tend
to be encrypted.

char *	PEM_ASN1_read_bio(char *(*d2i)(),char *name,BIO *fp,
	char **x,int (*cb)());
Same as PEM_ASN1_read() except using a BIO.  This is called by
PEM_ASN1_read().

int	PEM_ASN1_write(int (*i2d)(),char *name,FILE *fp,char *x,EVP_CIPHER *enc,
		unsigned char *kstr,int klen,int (*callback)());

int	PEM_ASN1_write_bio(int (*i2d)(),char *name,BIO *fp,
		char *x,EVP_CIPHER *enc,unsigned char *kstr,int klen,
		int (*callback)());

int ASN1_sign(int (*i2d)(), X509_ALGOR *algor1, X509_ALGOR *algor2,
	ASN1_BIT_STRING *signature, char *data, RSA *rsa, EVP_MD *type);
int ASN1_verify(int (*i2d)(), X509_ALGOR *algor1,
	ASN1_BIT_STRING *signature,char *data, RSA *rsa);

int ASN1_BIT_STRING_cmp(ASN1_BIT_STRING *a, ASN1_BIT_STRING *b);
ASN1_BIT_STRING *ASN1_BIT_STRING_type_new(int type );

int ASN1_UTCTIME_check(ASN1_UTCTIME *a);
void ASN1_UTCTIME_print(BIO *fp,ASN1_UTCTIME *a);
ASN1_UTCTIME *ASN1_UTCTIME_dup(ASN1_UTCTIME *a);

ASN1_BIT_STRING *d2i_asn1_print_type(ASN1_BIT_STRING **a,unsigned char **pp,
		long length,int type);

int		i2d_ASN1_SET(STACK *a, unsigned char **pp,
			int (*func)(), int ex_tag, int ex_class);
STACK *		d2i_ASN1_SET(STACK **a, unsigned char **pp, long length,
			char *(*func)(), int ex_tag, int ex_class);

int i2a_ASN1_OBJECT(BIO *bp,ASN1_OBJECT *object);
int i2a_ASN1_INTEGER(BIO *bp, ASN1_INTEGER *a);
int a2i_ASN1_INTEGER(BIO *bp,ASN1_INTEGER *bs,char *buf,int size);

int ASN1_INTEGER_set(ASN1_INTEGER *a, long v);
long ASN1_INTEGER_get(ASN1_INTEGER *a);
ASN1_INTEGER *BN_to_ASN1_INTEGER(BIGNUM *bn, ASN1_INTEGER *ai);
BIGNUM *ASN1_INTEGER_to_BN(ASN1_INTEGER *ai,BIGNUM *bn);

/* given a string, return the correct type.  Max is the maximum number
 * of bytes to parse.  It stops parsing when 'max' bytes have been
 * processed or a '\0' is hit */
int ASN1_PRINTABLE_type(unsigned char *s,int max);

void ASN1_parse(BIO *fp,unsigned char *pp,long len);

int i2d_ASN1_bytes(ASN1_BIT_STRING *a, unsigned char **pp, int tag, int class);
ASN1_BIT_STRING *d2i_ASN1_bytes(ASN1_OCTET_STRING **a, unsigned char **pp,
	long length, int Ptag, int Pclass);

/* PARSING */
int asn1_Finish(ASN1_CTX *c);

/* SPECIALS */
int ASN1_get_object(unsigned char **pp, long *plength, int *ptag,
	int *pclass, long omax);
int ASN1_check_infinite_end(unsigned char **p,long len);
void ASN1_put_object(unsigned char **pp, int constructed, int length,
	int tag, int class);
int ASN1_object_size(int constructed, int length, int tag);

X509 *	X509_get_cert(CERTIFICATE_CTX *ctx,X509_NAME * name,X509 *tmp_x509);
int  	X509_add_cert(CERTIFICATE_CTX *ctx,X509 *);

char *	X509_cert_verify_error_string(int n);
int 	X509_add_cert_file(CERTIFICATE_CTX *c,char *file, int type);
char *	X509_gmtime (char *s, long adj);
int	X509_add_cert_dir (CERTIFICATE_CTX *c,char *dir, int type);
int	X509_load_verify_locations (CERTIFICATE_CTX *ctx,
		char *file_env, char *dir_env);
int	X509_set_default_verify_paths(CERTIFICATE_CTX *cts);
X509 *	X509_new_D2i_X509(int len, unsigned char *p);
char *	X509_get_default_cert_area(void );
char *	X509_get_default_cert_dir(void );
char *	X509_get_default_cert_file(void );
char *	X509_get_default_cert_dir_env(void );
char *	X509_get_default_cert_file_env(void );
char *	X509_get_default_private_dir(void );
X509_REQ *X509_X509_TO_req(X509 *x, RSA *rsa);
int	X509_cert_verify(CERTIFICATE_CTX *ctx,X509 *xs, int (*cb)()); 

CERTIFICATE_CTX *CERTIFICATE_CTX_new();
void CERTIFICATE_CTX_free(CERTIFICATE_CTX *c);

void X509_NAME_print(BIO *fp, X509_NAME *name, int obase);
int		X509_print_fp(FILE *fp,X509 *x);
int		X509_print(BIO *fp,X509 *x);

X509_INFO *	X509_INFO_new(void);
void		X509_INFO_free(X509_INFO *a);

char *		X509_NAME_oneline(X509_NAME *a);

#define X509_verify(x,rsa)
#define X509_REQ_verify(x,rsa)
#define X509_CRL_verify(x,rsa)

#define X509_sign(x,rsa,md)
#define X509_REQ_sign(x,rsa,md)
#define X509_CRL_sign(x,rsa,md)

#define X509_dup(x509)
#define d2i_X509_fp(fp,x509)
#define i2d_X509_fp(fp,x509)
#define d2i_X509_bio(bp,x509)
#define i2d_X509_bio(bp,x509)

#define X509_CRL_dup(crl)
#define d2i_X509_CRL_fp(fp,crl)
#define i2d_X509_CRL_fp(fp,crl)
#define d2i_X509_CRL_bio(bp,crl)
#define i2d_X509_CRL_bio(bp,crl)

#define X509_REQ_dup(req)
#define d2i_X509_REQ_fp(fp,req)
#define i2d_X509_REQ_fp(fp,req)
#define d2i_X509_REQ_bio(bp,req)
#define i2d_X509_REQ_bio(bp,req)

#define RSAPrivateKey_dup(rsa)
#define d2i_RSAPrivateKey_fp(fp,rsa)
#define i2d_RSAPrivateKey_fp(fp,rsa)
#define d2i_RSAPrivateKey_bio(bp,rsa)
#define i2d_RSAPrivateKey_bio(bp,rsa)

#define X509_NAME_dup(xn)
#define X509_NAME_ENTRY_dup(ne)

void X509_REQ_print_fp(FILE *fp,X509_REQ *req);
void X509_REQ_print(BIO *fp,X509_REQ *req);

RSA *X509_REQ_extract_key(X509_REQ *req);
RSA *X509_extract_key(X509 *x509);

int		X509_issuer_and_serial_cmp(X509 *a, X509 *b);
unsigned long	X509_issuer_and_serial_hash(X509 *a);

X509_NAME *	X509_get_issuer_name(X509 *a);
int		X509_issuer_name_cmp(X509 *a, X509 *b);
unsigned long	X509_issuer_name_hash(X509 *a);

X509_NAME *	X509_get_subject_name(X509 *a);
int		X509_subject_name_cmp(X509 *a,X509 *b);
unsigned long	X509_subject_name_hash(X509 *x);

int		X509_NAME_cmp (X509_NAME *a, X509_NAME *b);
unsigned long	X509_NAME_hash(X509_NAME *x);