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diff --git a/crypto/openssl/README.ASN1 b/crypto/openssl/README.ASN1 deleted file mode 100644 index 11bcfaf..0000000 --- a/crypto/openssl/README.ASN1 +++ /dev/null @@ -1,187 +0,0 @@ - -OpenSSL ASN1 Revision -===================== - -This document describes some of the issues relating to the new ASN1 code. - -Previous OpenSSL ASN1 problems -============================= - -OK why did the OpenSSL ASN1 code need revising in the first place? Well -there are lots of reasons some of which are included below... - -1. The code is difficult to read and write. For every single ASN1 structure -(e.g. SEQUENCE) four functions need to be written for new, free, encode and -decode operations. This is a very painful and error prone operation. Very few -people have ever written any OpenSSL ASN1 and those that have usually wish -they hadn't. - -2. Partly because of 1. the code is bloated and takes up a disproportionate -amount of space. The SEQUENCE encoder is particularly bad: it essentially -contains two copies of the same operation, one to compute the SEQUENCE length -and the other to encode it. - -3. The code is memory based: that is it expects to be able to read the whole -structure from memory. This is fine for small structures but if you have a -(say) 1Gb PKCS#7 signedData structure it isn't such a good idea... - -4. The code for the ASN1 IMPLICIT tag is evil. It is handled by temporarily -changing the tag to the expected one, attempting to read it, then changing it -back again. This means that decode buffers have to be writable even though they -are ultimately unchanged. This gets in the way of constification. - -5. The handling of EXPLICIT isn't much better. It adds a chunk of code into -the decoder and encoder for every EXPLICIT tag. - -6. APPLICATION and PRIVATE tags aren't even supported at all. - -7. Even IMPLICIT isn't complete: there is no support for implicitly tagged -types that are not OPTIONAL. - -8. Much of the code assumes that a tag will fit in a single octet. This is -only true if the tag is 30 or less (mercifully tags over 30 are rare). - -9. The ASN1 CHOICE type has to be largely handled manually, there aren't any -macros that properly support it. - -10. Encoders have no concept of OPTIONAL and have no error checking. If the -passed structure contains a NULL in a mandatory field it will not be encoded, -resulting in an invalid structure. - -11. It is tricky to add ASN1 encoders and decoders to external applications. - -Template model -============== - -One of the major problems with revision is the sheer volume of the ASN1 code. -Attempts to change (for example) the IMPLICIT behaviour would result in a -modification of *every* single decode function. - -I decided to adopt a template based approach. I'm using the term 'template' -in a manner similar to SNACC templates: it has nothing to do with C++ -templates. - -A template is a description of an ASN1 module as several constant C structures. -It describes in a machine readable way exactly how the ASN1 structure should -behave. If this template contains enough detail then it is possible to write -versions of new, free, encode, decode (and possibly others operations) that -operate on templates. - -Instead of having to write code to handle each operation only a single -template needs to be written. If new operations are needed (such as a 'print' -operation) only a single new template based function needs to be written -which will then automatically handle all existing templates. - -Plans for revision -================== - -The revision will consist of the following steps. Other than the first two -these can be handled in any order. - -o Design and write template new, free, encode and decode operations, initially -memory based. *DONE* - -o Convert existing ASN1 code to template form. *IN PROGRESS* - -o Convert an existing ASN1 compiler (probably SNACC) to output templates -in OpenSSL form. - -o Add support for BIO based ASN1 encoders and decoders to handle large -structures, initially blocking I/O. - -o Add support for non blocking I/O: this is quite a bit harder than blocking -I/O. - -o Add new ASN1 structures, such as OCSP, CRMF, S/MIME v3 (CMS), attribute -certificates etc etc. - -Description of major changes -============================ - -The BOOLEAN type now takes three values. 0xff is TRUE, 0 is FALSE and -1 is -absent. The meaning of absent depends on the context. If for example the -boolean type is DEFAULT FALSE (as in the case of the critical flag for -certificate extensions) then -1 is FALSE, if DEFAULT TRUE then -1 is TRUE. -Usually the value will only ever be read via an API which will hide this from -an application. - -There is an evil bug in the old ASN1 code that mishandles OPTIONAL with -SEQUENCE OF or SET OF. These are both implemented as a STACK structure. The -old code would omit the structure if the STACK was NULL (which is fine) or if -it had zero elements (which is NOT OK). This causes problems because an empty -SEQUENCE OF or SET OF will result in an empty STACK when it is decoded but when -it is encoded it will be omitted resulting in different encodings. The new code -only omits the encoding if the STACK is NULL, if it contains zero elements it -is encoded and empty. There is an additional problem though: because an empty -STACK was omitted, sometimes the corresponding *_new() function would -initialize the STACK to empty so an application could immediately use it, if -this is done with the new code (i.e. a NULL) it wont work. Therefore a new -STACK should be allocated first. One instance of this is the X509_CRL list of -revoked certificates: a helper function X509_CRL_add0_revoked() has been added -for this purpose. - -The X509_ATTRIBUTE structure used to have an element called 'set' which took -the value 1 if the attribute value was a SET OF or 0 if it was a single. Due -to the behaviour of CHOICE in the new code this has been changed to a field -called 'single' which is 0 for a SET OF and 1 for single. The old field has -been deleted to deliberately break source compatibility. Since this structure -is normally accessed via higher level functions this shouldn't break too much. - -The X509_REQ_INFO certificate request info structure no longer has a field -called 'req_kludge'. This used to be set to 1 if the attributes field was -(incorrectly) omitted. You can check to see if the field is omitted now by -checking if the attributes field is NULL. Similarly if you need to omit -the field then free attributes and set it to NULL. - -The top level 'detached' field in the PKCS7 structure is no longer set when -a PKCS#7 structure is read in. PKCS7_is_detached() should be called instead. -The behaviour of PKCS7_get_detached() is unaffected. - -The values of 'type' in the GENERAL_NAME structure have changed. This is -because the old code use the ASN1 initial octet as the selector. The new -code uses the index in the ASN1_CHOICE template. - -The DIST_POINT_NAME structure has changed to be a true CHOICE type. - -typedef struct DIST_POINT_NAME_st { -int type; -union { - STACK_OF(GENERAL_NAME) *fullname; - STACK_OF(X509_NAME_ENTRY) *relativename; -} name; -} DIST_POINT_NAME; - -This means that name.fullname or name.relativename should be set -and type reflects the option. That is if name.fullname is set then -type is 0 and if name.relativename is set type is 1. - -With the old code using the i2d functions would typically involve: - -unsigned char *buf, *p; -int len; -/* Find length of encoding */ -len = i2d_SOMETHING(x, NULL); -/* Allocate buffer */ -buf = OPENSSL_malloc(len); -if(buf == NULL) { - /* Malloc error */ -} -/* Use temp variable because &p gets updated to point to end of - * encoding. - */ -p = buf; -i2d_SOMETHING(x, &p); - - -Using the new i2d you can also do: - -unsigned char *buf = NULL; -int len; -len = i2d_SOMETHING(x, &buf); -if(len < 0) { - /* Malloc error */ -} - -and it will automatically allocate and populate a buffer with the -encoding. After this call 'buf' will point to the start of the -encoding which is len bytes long. |