NSS Sample Code Sample_1_Hashing

NSS Sample Code 1: Hashing a file.

This is an example program that demonstrates how to compute the hash of a file and save it to another file.  This program illustrates the use of NSS message APIs.

Sample Code 1

/* NSPR Headers */
#include <prprf.h>
#include <prtypes.h>
#include <plgetopt.h>
#include <prio.h>

/* NSS headers */
#include <secoid.h>
#include <secmodt.h>
#include <sechash.h>

typedef struct {
    const char *hashName;
    SECOidTag oid;
} NameTagPair;

/* The hash algorithms supported */
static const NameTagPair HASH_NAMES[] = {
    { "MD2", SEC_OID_MD2 },
    { "MD5", SEC_OID_MD5 },
    { "SHA1", SEC_OID_SHA1 },
    { "SHA256", SEC_OID_SHA256 },
    { "SHA384", SEC_OID_SHA384 },
    { "SHA512", SEC_OID_SHA512 }
};

/*
 * Maps a hash name to a SECOidTag.
 * Returns NULL if the name is not a supported algorithm
 */
static SECOidTag HashNameToOIDTag(const char *hashName)
{
    int i, nhashes = sizeof(HASH_NAMES);
    SECOidTag hashtag = SEC_OID_UNKNOWN;

    for (i = 0; i < nhashes; i++) {
        if (PORT_Strcasecmp(hashName, HASH_NAMES[i].hashName) == 0) {
            hashtag = HASH_NAMES[i].oid;
            break;
        }
    }
    return hashtag;
}

/*
 * Newline
 */
static void Newline(PRFileDesc* out) { PR_fprintf(out, "\n"); }

/*
 * PrintAsHex
 */
void PrintAsHex(PRFileDesc* out, unsigned char *data, unsigned int len)
{
    unsigned i;
    int column;
    unsigned int limit = 15;
    unsigned int level  = 1;

    column = level;
    if (!len) {
        PR_fprintf(out, "(empty)\n");
        return;
    }

    for (i = 0; i < len; i++) {
        if (i != len - 1) {
            PR_fprintf(out, "%02x:", data[i]);
            column += 3;
        } else {
            PR_fprintf(out, "%02x", data[i]);
            column += 2;
            break;
        }
        if (column > 76 || (i % 16 == limit)) {
            Newline(out);
            column = level;
            limit = i % 16;
        }
    }
    if (column != level) {
        Newline(out);
    }
}

/*
 * Prints a usage message and exits
 */
static void Usage(const char *progName)
{
    int htype;
    int HASH_AlgTOTAL = sizeof(HASH_NAMES) / sizeof(HASH_NAMES[0]);

    fprintf(stderr, "Usage:  %s -t type [ < input ] [ > output ]\n", progName);
    fprintf(stderr, "%-20s Specify the digest method (must be one of\n",
            "-t type");
    fprintf(stderr, "%-20s ", "");
    for (htype = 0; htype < HASH_AlgTOTAL; htype++) {
        fprintf(stderr, HASH_NAMES[htype].hashName);
        if (htype == (HASH_AlgTOTAL - 2))
            fprintf(stderr, " or ");
        else if (htype != (HASH_AlgTOTAL - 1))
            fprintf(stderr, ", ");
    }
    fprintf(stderr, " (case ignored))\n");
    fprintf(stderr, "%-20s Define an input file to use (default is stdin)\n",
            "< input");
    fprintf(stderr, "%-20s Define an output file to use (default is stdout)\n",
            "> output");
    exit(-1);
}

/*
 * Check for the missing arguments 
 */
static void PrintMsgAndExit(const char *progName, char opt)
{
    fprintf(stderr, "%s: option -%c requires an argument\n", progName, opt);
    Usage(progName);
}

#define REQUIRE_ARG(opt,value) if (!(value)) PrintMsgAndExit(progName, opt)

/*
 * Digests a file according to the specified algorithm.
 * It writes out the digest as a hexadecimal string.
 */
static int DigestFile(PRFileDesc *outFile, PRFileDesc *inFile, SECOidTag hashOIDTag)
{
    unsigned int  nb;
    unsigned char ibuf[4096];
    unsigned char digest[64];
    unsigned int  len;
    unsigned int  digestLen;
    HASH_HashType hashType;
    HASHContext   *hashContext = NULL;

    hashType    = HASH_GetHashTypeByOidTag(hashOIDTag);
    hashContext = HASH_Create(hashType);
    if (hashContext == NULL) {
        return SECFailure;
    }

    do {

        HASH_Begin(hashContext);

        /* Incrementally hash the file contents */
        while ((nb = PR_Read(inFile, ibuf, sizeof(ibuf))) > 0) {
            HASH_Update(hashContext, ibuf, nb);
        }

        HASH_End(hashContext, digest, &len, 64);

        /*  Normally we would write it out in binary with
         *  nb = PR_Write(outFile, digest, len);
         *  but for illustration let's print it in hex.
         */
        PrintAsHex(outFile, digest, len);

    } while (0);

    /* cleanup */
    if (hashContext != NULL)
        HASH_Destroy(hashContext);

    return SECSuccess;
}

/*
 * This sample computes the hash of a file and saves it
 * to another file. It illustrates the use of NSS message
 * APIs.
 */
int main(int argc, char **argv)
{
    SECOidTag     hashOIDTag;
    PLOptState    *optstate;
    PLOptStatus   status;
    SECStatus     rv;
    char          *hashName  = NULL;
    char          *progName = strrchr(argv[0], '/');

    progName = progName ? progName + 1 : argv[0];

    rv = NSS_NoDB_Init("/tmp");
    if (rv != SECSuccess) {
        fprintf(stderr, "%s: NSS_Init failed in directory %s\n",
                progName, "/tmp");
        return -1;
    }

    /* Parse command line arguments */
    optstate = PL_CreateOptState(argc, argv, "t:");
    while ((status = PL_GetNextOpt(optstate)) == PL_OPT_OK) {
        switch (optstate->option) {
        case 't':
            REQUIRE_ARG(optstate->option, optstate->value);
            hashName = strdup(optstate->value);
            break;
        }
    }

    if (!hashName)
        Usage(progName);

    /* convert and validate */
    hashOIDTag = HashNameToOIDTag(hashName);
    if (hashOIDTag == SEC_OID_UNKNOWN) {
        fprintf(stderr, "%s: invalid digest type - %s\n", progName, hashName);
        Usage(progName);
    }

    /* Digest it and print the result */
    rv = DigestFile(PR_STDOUT, PR_STDIN, hashOIDTag);
    if (rv != SECSuccess) {
        fprintf(stderr, "%s: problem digesting data (%d)\n",
                progName, PORT_GetError());
    }

    rv = NSS_Shutdown();
    if (rv != SECSuccess) {
        exit(-1);
    }

    return 0;
}

</sechash.h></secmodt.h></secoid.h></prio.h></plgetopt.h></prtypes.h></prprf.h>