I had a string CN=myserver,O=test,C=us in a certificate, which has been encoded

Offset   :                                       EBCDIC          ASCII 
00000000 : 302F310B 30090603 55040613 02757331  ................ 0/1.0...U....us1  
00000010 : 0D300B06 0355040A 13047465 73743111  ................ .0...U....test1.  
00000020 : 300F0603 55040313 086D7973 65727665  ........._`..... 0...U....myserve  
00000030 : 72                                  .                r                 
    

where you can see the encoded string in ASCII on the right. How do I extract the string CN=myserver,O=test,C=us from this?

This format is used for Subjects and Issuers (and other types).

The hex string has an ASN.1 encoding. It usually starts with a 0x30. See here for a good introduction to ASN.1 encoding.

• 30 means this is a sequence
• 2f is the length of the data following
• etc

On z/OS you can use system ssl to decode this back to a printable string. You need two steps.

1. Convert to internal format,
2. Create the printable EBCDIC string from the internal format.

Step1 create internal format of the data

#pragma runopts(POSIX(ON)) 
#include <gskcms.h> 
#include <gskssl.h>  
void x509_to_string(char * pData, // pointer to the data
                     int lData)    // length of the data
{ 
   x509_name    X509;   // internal format.
   int rc; 
   gsk_buffer cert;     // intermediate format
   if (lData == 0) 
   { 
      printf("no data"); 
      return; 
   } 
   cert.length=   lData; 
   cert.data  =   pData ; 
   // convert from 0x302F310B 30090603 to internal 
   rc = gsk_decode_name( 
       & cert, 
       & X509); 
   if ( rc != 0) 
   { 
     //use gsk_strerror(rc) to return a string.
     printf("\nInternal error:gsk_decode_name %s\n", 
                  gsk_strerror(rc)); 
     return; 
   } 

Convert from internal format to an EBCDIC string.

   char * pName ;       // output value   
   // convert from internal to CN=COLIN,C=GB 
   rc = gsk_name_to_dn( 
              &X509, 
              &pName); 
   // free the intermediate value regardless of rc
   gsk_free_name(&X509); 
   if ( rc != 0) 
     { 
       printf("\nInternal error:gsk_name_dn %s\n", 
                    gsk_strerror(rc)); 
       return; 
     } 
   printf("%s.",pName); 

   //free the string 
   gsk_free_string(pName); 
} 

Convert from EBCDIC string to intermediate or certificate format.

There are the reverse functions.

• gsk_dn_to_name( pName, &X509);
• rc = gsk_encode_name( &X509, & cert);

Both C=GB,CN=colin and c=GB,cn=colin produce

00000000 : 301D310E 300C0603 55040313 05636F6C …………..?% 0.1.0…U….col
00000010 : 696E310B 30090603 55040613 024742 .>…………. in1.0…U….GB

JCL

I needed binder input options.

INCLUDE GSK(GSKCMS31) 
INCLUDE GSK(GSKSSL) 

and JCL

//COMPILE  EXEC PROC=EDCCB, 
//       LIBPRFX=&LIBPRFX, 
//       CPARM='OPTFILE(DD:SYSOPTF)', 
// BPARM='SIZE=(900K,124K),RENT,LIST,RMODE=ANY,AMODE=31,AC=1' 
//COMPILE.SYSLIB DD DISP=SHR,DSN=&LIBPRFX..SCEEH.SYS.H 
//               DD DISP=SHR,DSN=&LIBPRFX..SCEEH.H 
//               DD DISP=SHR,DSN=SYS1.SIEAHDR.H 
...
//COMPILE.SYSIN  DD DSN=&SOURCE(&PROG),DISP=SHR 
//COMPILE.SYS    DD DISP=SHR,DSN=&LIBPRFX..SCEEH.SYS.H 
//COMPILE.SYSOPTF DD DISP=SHR,DSN=&SOURCE(CCOPTS) 
//* 
//* Bind the module 
//* 
//BIND.SYSLMOD DD DISP=SHR,DSN=&LOADLIB(&PROG) 
//BIND.SYSLIB  DD DISP=SHR,DSN=&LIBPRFX..SCEELKED 
//             DD DISP=SHR,DSN=SYS1.SIEALNKE 
//BIND.GSK     DD DISP=SHR,DSN=SYS1.SIEALNKE 
...
//BIND.SYSIN DD DISP=SHR,DSN=&SOURCE(&BINDOPTS) 

Where the gskcms.h and gskssl.h are in DSN=SYS1.SIEAHDR.H or /usr/include/, and the binder stubs are in DSN=SYS1.SIEALNKE.