#include <CSP_WinDef.h>
#include <CSP_WinCrypt.h>
#include <stdio.h>
#include <stdlib.h>

int main() {
char *name = "pages.decoded";
FILE *fp = fopen(name, "r");

fseek(fp, 0L, SEEK_END);
int filesize = ftell(fp);
rewind(fp);

char *buffer = malloc(filesize);
fread(buffer, filesize, 1, fp);

fclose(fp);

DWORD size = 0;
if (!CryptDecodeObject(X509_ASN_ENCODING, X509_SEQUENCE_OF_ANY, buffer, filesize, 0, NULL, &size)) {
printf("Error: 0x%x\n", GetLastError());
} else {
printf("Size: %d\n", size);
}
}

gcc -L/opt/cprocsp/lib/ia32 -lcapi20 -I/opt/cprocsp/include/cpcsp test.c

guiDumpASN-ng выдает: