Android培训班(62)dex文件格式3

SHA－1签名字段    从dex文件头里，已经看到前面有一个4字节的字段检验码了，那为什么又需要一个SHA－1签名字段呢？ 这不是重复了吗？起初始看来，好像是有点重复，可是仔细考虑一下，这样设计，还是比较高明的。因为dex文件的大小，一般都不是很小，简单的应用程序都有几十K大小，这么多数据使用一个4字节的检验码，重复的机率还是有的，也就是说当文件里的数据修改了，还是检验不出来。那么这时，检验码就失去了作用，需要使用更加强大的检验码，这就是SHA－1，它是20个字节，比前面的检验码多了16个字节，理论上就强大了很多，几乎不会不同的文件计算出来的检验是一样的了。设计两个检验码的目的，就是先使用第一个检验码进行快速检查，这样可以先把简单出错的dex文件丢掉了。接着再使用第二个复杂的检验码进行复杂计算，验证文件是否完整，这样确保执行的文件完整和安全。
SHA（Secure Hash Algorithm, 安全散列算法）是美国国家安全局设计，美国国家标准与技术研究院发布的一系列密码散列函数。SHA－1看起来和MD5算法很像，也许是Ron Rivest在SHA－1的设计中起了一定的作用。SHA－1的内部比MD5更强，其摘要比MD5的16字节长4个字节，这个算法成功经受了密码分析专家的攻击，也因而受到密码学界的广泛推崇。这个算法，在目前网络上的签名，大名顶顶的BT软件里就大量使用，比如在BT里要计算是否同一个种子时，就是使用判断不同的签名。比如验证同一份8G的电影从几千BT用户那里下载，也不会出现错误的数据，导致电影不播放。
在Android系统使用的SHA－1算法源码如下：
/*
 * Tweaked in various ways for Google/Android:
 *  - Changed from .cpp to .c.
 *  - Made argument to SHA1Update a const pointer, and enabled
 *    SHA1HANDSOFF.  This incurs a speed penalty but prevents us from
 *    trashing the input.
 *  - Include <endian.h> to get endian info.
 *  - Split a small piece into a header file.
 */


/*
sha1sum: inspired by md5sum.


SHA-1 in C
By Steve Reid <[email protected]>
100% Public Domain


-----------------
Modified 7/98 
By James H. Brown <[email protected]>
Still 100% Public Domain


bit machines
Routine SHA1Update changed from
    void SHA1Update(SHA1_CTX* context, unsigned char* data,
      unsigned int len)
to
    void SHA1Update(SHA1_CTX* context, unsigned char* data,
      unsigned long len)


The 'len' parameter was declared an int which works fine on 32
bit machines. However, on 16 bit machines an int is too small
for the shifts being done against it.  This caused the hash
function to generate incorrect values if len was greater than
8191 (8K - 1) due to the 'len << 3' on line 3 of SHA1Update().


Since the file IO in main() reads 16K at a time, any file 8K or
larger would be guaranteed to generate the wrong hash (e.g.
Test Vector #3, a million "a"s).


I also changed the declaration of variables i & j in SHA1Update
to unsigned long from unsigned int for the same reason.


These changes should make no difference to any 32 bit
implementations since an int and a long are the same size in
those environments.


--
I also corrected a few compiler warnings generated by Borland
C.
1. Added #include <process.h> for exit() prototype
2. Removed unused variable 'j' in SHA1Final
3. Changed exit(0) to return(0) at end of main.


ALL changes I made can be located by searching for comments
containing 'JHB'


-----------------
Modified 13 August 2000
By Michael Paul Johnson <[email protected]>
Still 100% Public Domain


Changed command line syntax, added feature to automatically
check files against their previous SHA-1 check values, kind of
like md5sum does. Added functions hexval, verifyfile,
and sha1file. Rewrote main().
-----------------


Test Vectors (from FIPS PUB 180-1)
"abc"
  A9993E36 4706816A BA3E2571 7850C26C 9CD0D89D
"abcdbcdecdefdefgefghfghighijhijkijkljklmklmnlmnomnopnopq"
  84983E44 1C3BD26E BAAE4AA1 F95129E5 E54670F1
A million repetitions of "a"
  34AA973C D4C4DAA4 F61EEB2B DBAD2731 6534016F
*/


#define SHA1HANDSOFF    /*Copies data before messing with it.*/


/*#define CMDLINE        * include main() and file processing */


#include "sha1.h"


#include <stdio.h>
#include <string.h>
#ifdef __BORLANDC__
#include <dir.h>
#include <dos.h>
#include <process.h>   /*  prototype for exit() - JHB
               needed for Win32, but chokes Linux - MPJ */
#define X_LITTLE_ENDIAN /* This should be #define'd if true.*/
#else
# include <unistd.h>
# include <stdlib.h>
//# include <endian.h>


#include "DexFile.h"    // want common byte ordering def


# if __BYTE_ORDER == __LITTLE_ENDIAN
#  define X_LITTLE_ENDIAN
# endif
#endif
#include <ctype.h>


#define LINESIZE 2048


static void SHA1Transform(unsigned long state[5],
    const unsigned char buffer[64]);


#define rol(value,bits) \
 (((value)<<(bits))|((value)>>(32-(bits))))


/* blk0() and blk() perform the initial expand. */
/* I got the idea of expanding during the round function from
   SSLeay */
#ifdef X_LITTLE_ENDIAN
#define blk0(i) (block->l[i]=(rol(block->l[i],24)&0xFF00FF00) \
    |(rol(block->l[i],8)&0x00FF00FF))
#else
#define blk0(i) block->l[i]
#endif
#define blk(i) (block->l[i&15] = rol(block->l[(i+13)&15]^block->l[(i+8)&15] \
    ^block->l[(i+2)&15]^block->l[i&15],1))


/* (R0+R1), R2, R3, R4 are the different operations used in SHA1 */
#define R0(v,w,x,y,z,i) z+=((w&(x^y))^y)+blk0(i)+0x5A827999+rol(v,5);w=rol(w,30);
#define R1(v,w,x,y,z,i) z+=((w&(x^y))^y)+blk(i)+0x5A827999+rol(v,5);w=rol(w,30);
#define R2(v,w,x,y,z,i) z+=(w^x^y)+blk(i)+0x6ED9EBA1+rol(v,5);w=rol(w,30);
#define R3(v,w,x,y,z,i) z+=(((w|x)&y)|(w&x))+blk(i)+0x8F1BBCDC+rol(v,5);w=rol(w,30);
#define R4(v,w,x,y,z,i) z+=(w^x^y)+blk(i)+0xCA62C1D6+rol(v,5);w=rol(w,30);




/* Hash a single 512-bit block. This is the core of the algorithm. */


static void SHA1Transform(unsigned long state[5],
    const unsigned char buffer[64])
{
unsigned long a, b, c, d, e;
typedef union {
    unsigned char c[64];
    unsigned long l[16];
} CHAR64LONG16;
CHAR64LONG16* block;
#ifdef SHA1HANDSOFF
static unsigned char workspace[64];
    block = (CHAR64LONG16*)workspace;
    memcpy(block, buffer, 64);
#else
    block = (CHAR64LONG16*)buffer;
#endif
    /* Copy context->state[] to working vars */
    a = state[0];
    b = state[1];
    c = state[2];
    d = state[3];
    e = state[4];
    /* 4 rounds of 20 operations each. Loop unrolled. */
    R0(a,b,c,d,e, 0); R0(e,a,b,c,d, 1); R0(d,e,a,b,c, 2);
    R0(c,d,e,a,b, 3); R0(b,c,d,e,a, 4); R0(a,b,c,d,e, 5);
    R0(e,a,b,c,d, 6); R0(d,e,a,b,c, 7); R0(c,d,e,a,b, 8);
    R0(b,c,d,e,a, 9); R0(a,b,c,d,e,10); R0(e,a,b,c,d,11);
    R0(d,e,a,b,c,12); R0(c,d,e,a,b,13); R0(b,c,d,e,a,14);
    R0(a,b,c,d,e,15); R1(e,a,b,c,d,16); R1(d,e,a,b,c,17);
    R1(c,d,e,a,b,18); R1(b,c,d,e,a,19); R2(a,b,c,d,e,20);
    R2(e,a,b,c,d,21); R2(d,e,a,b,c,22); R2(c,d,e,a,b,23);
    R2(b,c,d,e,a,24); R2(a,b,c,d,e,25); R2(e,a,b,c,d,26);
    R2(d,e,a,b,c,27); R2(c,d,e,a,b,28); R2(b,c,d,e,a,29);
    R2(a,b,c,d,e,30); R2(e,a,b,c,d,31); R2(d,e,a,b,c,32);
    R2(c,d,e,a,b,33); R2(b,c,d,e,a,34); R2(a,b,c,d,e,35);
    R2(e,a,b,c,d,36); R2(d,e,a,b,c,37); R2(c,d,e,a,b,38);
    R2(b,c,d,e,a,39); R3(a,b,c,d,e,40); R3(e,a,b,c,d,41);
    R3(d,e,a,b,c,42); R3(c,d,e,a,b,43); R3(b,c,d,e,a,44);
    R3(a,b,c,d,e,45); R3(e,a,b,c,d,46); R3(d,e,a,b,c,47);
    R3(c,d,e,a,b,48); R3(b,c,d,e,a,49); R3(a,b,c,d,e,50);
    R3(e,a,b,c,d,51); R3(d,e,a,b,c,52); R3(c,d,e,a,b,53);
    R3(b,c,d,e,a,54); R3(a,b,c,d,e,55); R3(e,a,b,c,d,56);
    R3(d,e,a,b,c,57); R3(c,d,e,a,b,58); R3(b,c,d,e,a,59);
    R4(a,b,c,d,e,60); R4(e,a,b,c,d,61); R4(d,e,a,b,c,62);
    R4(c,d,e,a,b,63); R4(b,c,d,e,a,64); R4(a,b,c,d,e,65);
    R4(e,a,b,c,d,66); R4(d,e,a,b,c,67); R4(c,d,e,a,b,68);
    R4(b,c,d,e,a,69); R4(a,b,c,d,e,70); R4(e,a,b,c,d,71);
    R4(d,e,a,b,c,72); R4(c,d,e,a,b,73); R4(b,c,d,e,a,74);
    R4(a,b,c,d,e,75); R4(e,a,b,c,d,76); R4(d,e,a,b,c,77);
    R4(c,d,e,a,b,78); R4(b,c,d,e,a,79);


    /* Add the working vars back into context.state[] */
    state[0] += a;
    state[1] += b;
    state[2] += c;
    state[3] += d;
    state[4] += e;
    /* Wipe variables */
/*    a = b = c = d = e = 0; Nice try, but the compiler
optimizes this out, anyway, and it produces an annoying
warning. */
}




/* SHA1Init - Initialize new context */


void SHA1Init(SHA1_CTX* context)
{
    /* SHA1 initialization constants */
    context->state[0] = 0x67452301;
    context->state[1] = 0xEFCDAB89;
    context->state[2] = 0x98BADCFE;
    context->state[3] = 0x10325476;
    context->state[4] = 0xC3D2E1F0;
    context->count[0] = context->count[1] = 0;
}




/* Run your data through this. */


void SHA1Update(SHA1_CTX* context, const unsigned char* data,
    unsigned long len)  /* JHB */
{
    unsigned long i, j; /* JHB */


    j = (context->count[0] >> 3) & 63;
    if ((context->count[0] += len << 3) < (len << 3))
        context->count[1]++;
    context->count[1] += (len >> 29);
    if ((j + len) > 63)
    {
        memcpy(&context->buffer[j], data, (i = 64-j));
        SHA1Transform(context->state, context->buffer);
        for ( ; i + 63 < len; i += 64) {
            SHA1Transform(context->state, &data[i]);
        }
        j = 0;
    }
    else
        i = 0;
    memcpy(&context->buffer[j], &data[i], len - i);
}




/* Add padding and return the message digest. */


void SHA1Final(unsigned char digest[HASHSIZE], SHA1_CTX*
context)
{
unsigned long i;    /* JHB */
unsigned char finalcount[8];


    for (i = 0; i < 8; i++)
    {
        finalcount[i] = (unsigned char)((context->count[(i>=4?
            0:1)]>>((3-(i&3))*8))&255);
        /* Endian independent */
    }
    SHA1Update(context, (unsigned char *)"\200", 1);
    while ((context->count[0] & 504) != 448) {
        SHA1Update(context, (unsigned char *)"\0", 1);
    }
    SHA1Update(context, finalcount, 8);
    /* Should cause a SHA1Transform() */
    for (i = 0; i < HASHSIZE; i++) {
        digest[i] = (unsigned char)
         ((context->state[i>>2] >> ((3-(i & 3)) * 8) ) & 255);
    }
    /* Wipe variables */
    memset(context->buffer, 0, 64);
    memset(context->state, 0, HASHSIZE);
    memset(context->count, 0, 8);
    memset(&finalcount, 0, 8);
#ifdef SHA1HANDSOFF
    /* make SHA1Transform overwrite it's own static vars */
    SHA1Transform(context->state, context->buffer);
#endif
}






#ifdef CMDLINE


/* sha1file computes the SHA-1 hash of the named file and puts
   it in the 20-byte array digest. If fname is NULL, stdin is
   assumed.
*/
void sha1file(char *fname, unsigned char* digest)
{
    int bytesread;
    SHA1_CTX context;
    unsigned char buffer[16384];
    FILE* f;


    if (fname)
    {
        f = fopen(fname, "rb");
        if (!f)
        {
            fprintf(stderr, "Can't open %s\n", fname);
            memset(digest, 0, HASHSIZE);
            return;
        }
    }
    else
    {
        f = stdin;
    }
    SHA1Init(&context);
    while (!feof(f))
    {
        bytesread = fread(buffer, 1, 16384, f);
        SHA1Update(&context, buffer, bytesread);
    }
    SHA1Final(digest, &context);
    if (fname)
        fclose(f);
}


/* Convert ASCII hexidecimal digit to 4-bit value. */
unsigned char hexval(char c)
{
    unsigned char h;


    c = toupper(c);
    if (c >= 'A')
        h = c - 'A' + 10;
    else
        h = c - '0';
    return h;
}


/* Verify a file created with sha1sum by redirecting output
   to a file. */
int verifyfile(char *fname)
{
    int j, k;
    int found = 0;
    unsigned char digest[HASHSIZE];
    unsigned char expected_digest[HASHSIZE];
    FILE *checkfile;
    char checkline[LINESIZE];
    char *s;
    unsigned char err;


    checkfile = fopen(fname, "rt");
    if (!checkfile)
    {
        fprintf(stderr, "Can't open %s\n", fname);
        return(0);
    }
    do
    {
        s = fgets(checkline, LINESIZE, checkfile);
        if (s)
        {
            if ((strlen(checkline)>26)&&
                1 /*(!strncmp(checkline,"SHA1=", 5))*/)
            {
                /* Overwrite newline. */
                checkline[strlen(checkline)-1]=0;
                found = 1;


                /* Read expected check value. */
                for (k=0, j=5; k < HASHSIZE; k++)
                {
                    expected_digest[k]=hexval(checkline[j++]);
                    expected_digest[k]=(expected_digest[k]<<4)
                        +hexval(checkline[j++]);
                }


                /* Compute fingerprints */
                s = checkline+46;
                sha1file(s, digest);


                /* Compare fingerprints */
                err = 0;
                for (k=0; k<HASHSIZE; k++)
                    err |= digest[k]-
                        expected_digest[k];
                if (err)
                {
                    fprintf(stderr, "FAILED: %s\n"
                        " EXPECTED: ", s);
                    for (k=0; k<HASHSIZE; k++)
                        fprintf(stderr, "%02X",
                            expected_digest[k]);
                    fprintf(stderr,"\n    FOUND: ");
                    for (k=0; k<HASHSIZE; k++)
                        fprintf(stderr, "%02X", digest[k]);
                    fprintf(stderr, "\n");
                }
                else
                {
                    printf("OK: %s\n", s);
                }
            }
        }
    } while (s);
    return found;
}






void syntax(char *progname)
{
    printf("\nsyntax:\n"
     "%s [-c|-h][-q] file name[s]\n"
     "    -c = check files against previous check values\n"
     "    -g = generate SHA-1 check values (default action)\n"
     "    -h = display this help\n"
     "For example,\n"
     "sha1sum test.txt > check.txt\n"
     "generates check value for test.txt in check.txt, and\n"
     "sha1sum -c check.txt\n"
     "checks test.txt against the check value in check.txt\n",
     progname);
    exit(1);
}




/**********************************************************/


int main(int argc, char** argv)
{
    int i, j, k;
    int check = 0;
    int found = 0;
    unsigned char digest[HASHSIZE];
    unsigned char expected_digest[HASHSIZE];
    FILE *checkfile;
    char checkline[LINESIZE];
    char *s;
#ifdef __BORLANDC__
    struct ffblk f;
    int done;
    char path[MAXPATH];
    char drive[MAXDRIVE];
    char dir[MAXDIR];
    char name[MAXFILE];
    char ext[MAXEXT];
#endif
    unsigned char err;


    for (i = 1; i < argc; i++)
    {
        if (argv[i][0] == '-')
        {
            switch (argv[i][1])
            {
                case 'c':
                case 'C':
                    check = 1;
                    break;
                case 'g':
                case 'G':
                    check = 0;
                    break;
                default:
                    syntax(argv[0]);
            }
        }
    }


    for (i=1; i<argc; i++)
    {
        if (argv[i][0] != '-')
        {
#ifdef __BORLANDC__
            fnsplit(argv[i], drive, dir, name, ext);
            done = findfirst(argv[i], &f, FA_RDONLY |
                FA_HIDDEN|FA_SYSTEM|FA_ARCH);
             while (!done)
            {
                sprintf(path, "%s%s%s", drive, dir, f.ff_name);
                s = path;
#else
                s = argv[i];
#endif


                if (check)
                {   /* Check fingerprint file. */
                    found |= verifyfile(s);
                }
                else
                {   /* Generate fingerprints & write to
                       stdout. */
                    sha1file(s, digest);
                    //printf("SHA1=");
                    for (j=0; j<HASHSIZE; j++)
                        printf("%02x", digest[j]);
                    printf("  %s\n", s);
                    found = 1;
                }


#ifdef __BORLANDC__
                done = findnext(&f);
            }
#endif


        }
    }
    if (!found)
    {
        if (check)
        {
            fprintf(stderr,
                "No SHA1 lines found in %s\n",
                argv[i]);
        }
        else
        {
            fprintf(stderr, "No files checked.\n");
            syntax(argv[0]);
        }
    }
    return(0);  /* JHB */
}


#endif  /*CMDLINE*/