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Add BIO_read() (etc.) docs.

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Add an ASN1 FAQ because I'm sick of answering it :-)
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Dr. Stephen Henson 2000-09-09 00:59:37 +00:00
parent a652ffc4b5
commit c5a3b7e790
2 changed files with 56 additions and 0 deletions
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38
FAQ
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@ -10,6 +10,7 @@ OpenSSL - Frequently Asked Questions
* Why does the linker complain about undefined symbols?
* Where can I get a compiled version of OpenSSL?
* I've compiled a program under Windows and it crashes: why?
* How do I read or write a DER encoded buffer using the ASN1 functions?
* I've tried using <M_some_evil_pkcs12_macro> and I get errors why?
* I've called <some function> and it fails, why?
* I just get a load of numbers for the error output, what do they mean?
@ -182,6 +183,43 @@ otherwise the conflict will cause a program to crash: typically on the
first BIO related read or write operation.
* How do I read or write a DER encoded buffer using the ASN1 functions?
You have two options. You can either use a memory BIO in conjunction
with the i2d_XXX_bio() or d2i_XXX_bio() functions or you can use the
i2d_XXX(), d2i_XXX() functions directly. Since these are often the
cause of grief here are some code fragments using PKCS7 as an example:
unsigned char *buf, *p;
int len;
len = i2d_PKCS7(p7, NULL);
buf = OPENSSL_Malloc(len); /* or Malloc, error checking omitted */
p = buf;
i2d_PKCS7(p7, &p);
At this point buf contains the len bytes of the DER encoding of
p7.
The opposite assumes we already have len bytes in buf:
unsigned char *p;
p = buf;
p7 = d2i_PKCS7(NULL, &p, len);
At this point p7 contains a valid PKCS7 structure of NULL if an error
occurred. If an error occurred ERR_print_errors(bio) should give more
information.
The reason for the temporary variable 'p' is that the ASN1 functions
increment the passed pointer so it is ready to read or write the next
structure. This is often a cause of problems: without the temporary
variable the buffer pointer is changed to point just after the data
that has been read or written. This may well be uninitialized data
and attempts to free the buffer will have unpredictable results
because it no longer points to the same address.
* I've tried using <M_some_evil_pkcs12_macro> and I get errors why?
This usually happens when you try compiling something using the PKCS#12

18
doc/openssl.txt
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@ -355,6 +355,24 @@ that would not make sense. It does support an additional issuer:copy option
that will copy all the subject alternative name values from the issuer
certificate (if possible).
Example:
issuserAltName = issuer:copy
Authority Info Access.
The authority information access extension gives details about how to access
certain information relating to the CA. Its syntax is accessOID;location
where 'location' has the same syntax as subject alternative name (except
that email:copy is not supported). accessOID can be any valid OID but only
certain values are meaningful for example OCSP and caIssuers. OCSP gives the
location of an OCSP responder: this is used by Netscape PSM and other software.
Example:
authorityInfoAccess = OCSP;URI:http://ocsp.my.host/
authorityInfoAccess = caIssuers;URI:http://my.ca/ca.html
CRL distribution points.
This is a multi-valued extension that supports all the literal options of