source: trunk/Sparkle/SUDSAVerifier.m @ 1046

//
//  SUDSAVerifier.m
//  Sparkle
//
//  Created by Andy Matuschak on 3/16/06.
//  Copyright 2006 Andy Matuschak. All rights reserved.
//

// DSA stuff adapted from code provided by Allan Odgaard. Thanks, Allan!

#import "SUDSAVerifier.h"

#import <stdio.h>
#import <openssl/evp.h>
#import <openssl/bio.h>
#import <openssl/pem.h>
#import <openssl/rsa.h>
#import <openssl/sha.h>

long b64decode(unsigned char* str)
{
    unsigned char *cur, *start;
    int d, dlast, phase;
    unsigned char c;
    static int table[256] = {
        -1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,  /* 00-0F */
        -1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,  /* 10-1F */
        -1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,62,-1,-1,-1,63,  /* 20-2F */
        52,53,54,55,56,57,58,59,60,61,-1,-1,-1,-1,-1,-1,  /* 30-3F */
        -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9,10,11,12,13,14,  /* 40-4F */
        15,16,17,18,19,20,21,22,23,24,25,-1,-1,-1,-1,-1,  /* 50-5F */
        -1,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,  /* 60-6F */
        41,42,43,44,45,46,47,48,49,50,51,-1,-1,-1,-1,-1,  /* 70-7F */
        -1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,  /* 80-8F */
        -1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,  /* 90-9F */
        -1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,  /* A0-AF */
        -1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,  /* B0-BF */
        -1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,  /* C0-CF */
        -1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,  /* D0-DF */
        -1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,  /* E0-EF */
        -1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1   /* F0-FF */
    };
    
    d = dlast = phase = 0;
    start = str;
    for (cur = str; *cur != '\0'; ++cur )
    {
        if(*cur == '\n' || *cur == '\r'){phase = dlast = 0; continue;}
        d = table[(int)*cur];
        if(d != -1)
        {
            switch(phase)
            {
                case 0:
                    ++phase;
                    break;
                case 1:
                    c = ((dlast << 2) | ((d & 0x30) >> 4));
                    *str++ = c;
                    ++phase;
                    break;
                case 2:
                    c = (((dlast & 0xf) << 4) | ((d & 0x3c) >> 2));
                    *str++ = c;
                    ++phase;
                    break;
                case 3:
                    c = (((dlast & 0x03 ) << 6) | d);
                    *str++ = c;
                    phase = 0;
                    break;
            }
            dlast = d;
        }
    }
    *str = '\0';
    return str - start;
}

EVP_PKEY* load_dsa_key(char *key)
{
    EVP_PKEY* pkey = NULL;
    BIO *bio;
    if((bio = BIO_new_mem_buf(key, (int)strlen(key))))
    {
        DSA* dsa_key = 0;
        if(PEM_read_bio_DSA_PUBKEY(bio, &dsa_key, NULL, NULL))
        {
            if((pkey = EVP_PKEY_new()))
            {
                if(EVP_PKEY_assign_DSA(pkey, dsa_key) != 1)
                {
                    DSA_free(dsa_key);
                    EVP_PKEY_free(pkey);
                    pkey = NULL;
                }
            }
        }
        BIO_free(bio);
    }
    return pkey;
}

@implementation SUDSAVerifier

+ (BOOL)validatePath:(NSString *)path withEncodedDSASignature:(NSString *)encodedSignature withPublicDSAKey:(NSString *)pkeyString
{
    BOOL result = NO;
    if (!encodedSignature) { return NO; }
    if (!pkeyString) { return NO; }
    
    // Remove whitespace around each line of the key.
    NSMutableArray *pkeyTrimmedLines = [NSMutableArray array];
    NSEnumerator *pkeyLinesEnumerator = [[pkeyString componentsSeparatedByString:@"\n"] objectEnumerator];
    NSString *pkeyLine;
    while ((pkeyLine = [pkeyLinesEnumerator nextObject]) != nil)
    {
        [pkeyTrimmedLines addObject:[pkeyLine stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceCharacterSet]]];
    }
    pkeyString = [pkeyTrimmedLines componentsJoinedByString:@"\n"]; // Put them back together.

    EVP_PKEY* pkey = NULL;
    pkey = load_dsa_key((char *)[pkeyString UTF8String]);
    if (!pkey) { return NO; }

    // Now, the signature is in base64; we have to decode it into a binary stream.
    unsigned char *signature = (unsigned char *)[encodedSignature UTF8String];
    long length = b64decode(signature); // Decode the signature in-place and get the new length of the signature string.
    
    // We've got the signature, now get the file data.
    NSData *pathData = [NSData dataWithContentsOfFile:path];
    if (!pathData) { return NO; }
    
    // Hash the file with SHA-1.
    unsigned char md[SHA_DIGEST_LENGTH];
    SHA1([pathData bytes], [pathData length], md);
    
    // Actually verify the signature on the file.
    EVP_MD_CTX ctx;
    if(EVP_VerifyInit(&ctx, EVP_dss1()) == 1) // We're using DSA keys.
    {
        EVP_VerifyUpdate(&ctx, md, SHA_DIGEST_LENGTH);
        result = (EVP_VerifyFinal(&ctx, signature, (unsigned int)length, pkey) == 1);
    }
    
    EVP_PKEY_free(pkey);
    return result;
}

@end