enc_read.c

来自「Netscape公司提供的安全套接字层」· C语言 代码 · 共 143 行

/* enc_read.c */
/* Copyright (C) 1993 Eric Young - see README for more details */
#include <errno.h>
#include "des_locl.h"

/* This has some uglies in it but it works - even over sockets. */
extern int errno;
int des_rw_mode=DES_PCBC_MODE;

int des_enc_read(fd,buf,len,sched,iv)
int fd;
char *buf;
int len;
des_key_schedule sched;
des_cblock *iv;
    {
    /* data to be unencrypted */
    int net_num=0;
    unsigned char net[BSIZE];
    /* extra unencrypted data 
     * for when a block of 100 comes in but is des_read one byte at
     * a time. */
    static char unnet[BSIZE];
    static int unnet_start=0;
    static int unnet_left=0;
    int i;
    long num=0,rnum;
    unsigned char *p;

    /* left over data from last decrypt */
    if (unnet_left != 0)
        {
        if (unnet_left < len)
            {
            /* we still still need more data but will return
             * with the number of bytes we have - should always
             * check the return value */
            bcopy(&(unnet[unnet_start]),buf,unnet_left);
            /* eay 26/08/92 I had the next 2 lines
             * reversed :-( */
            i=unnet_left;
            unnet_start=unnet_left=0;
            }
        else
            {
            bcopy(&(unnet[unnet_start]),buf,len);
            unnet_start+=len;
            unnet_left-=len;
            i=len;
            }
        return(i);
        }

    /* We need to get more data. */
    if (len > MAXWRITE) len=MAXWRITE;

    /* first - get the length */
    net_num=0;
    while (net_num < HDRSIZE) 
        {
        i=read(fd,&(net[net_num]),HDRSIZE-net_num);
        if ((i == -1) && (errno == EINTR)) continue;
        if (i <= 0) return(0);
        net_num+=i;
        }

    /* we now have at net_num bytes in net */
    p=net;
    num=0;
    n2l(p,num);
    /* num should be rounded up to the next group of eight
     * we make sure that we have read a multiple of 8 bytes from the net.
     */
    if ((num > MAXWRITE) || (num < 0)) /* error */
        return(-1);
    rnum=(num < 8)?8:((num+7)/8*8);

    net_num=0;
    while (net_num < rnum)
        {
        i=read(fd,&(net[net_num]),rnum-net_num);
        if ((i == -1) && (errno == EINTR)) continue;
        if (i <= 0) return(0);
        net_num+=i;
        }

    /* Check if there will be data left over. */
    if (len < num)
        {
        if (des_rw_mode & DES_PCBC_MODE)
            pcbc_encrypt((des_cblock *)net,(des_cblock *)unnet,
                num,sched,iv,DES_DECRYPT);
        else
            cbc_encrypt((des_cblock *)net,(des_cblock *)unnet,
                num,sched,iv,DES_DECRYPT);
        bcopy(unnet,buf,len);
        unnet_start=len;
        unnet_left=num-len;

        /* The following line is done because we return num
         * as the number of bytes read. */
        num=len;
        }
    else
        {
        /* >output is a multiple of 8 byes, if len < rnum
         * >we must be careful.  The user must be aware that this
         * >routine will write more bytes than he asked for.
         * >The length of the buffer must be correct.
         * FIXED - Should be ok now 18-9-90 - eay */
        if (len < rnum)
            {
            char tmpbuf[BSIZE];

            if (des_rw_mode & DES_PCBC_MODE)
                pcbc_encrypt((des_cblock *)net,
                    (des_cblock *)tmpbuf,
                    num,sched,iv,DES_DECRYPT);
            else
                cbc_encrypt((des_cblock *)net,
                    (des_cblock *)tmpbuf,
                    num,sched,iv,DES_DECRYPT);

            /* eay 26/08/92 fix a bug that returned more
             * bytes than you asked for (returned len bytes :-( */
            bcopy(tmpbuf,buf,num);
            }
        else
            {
            if (des_rw_mode & DES_PCBC_MODE)
                pcbc_encrypt((des_cblock *)net,
                    (des_cblock *)buf,num,sched,iv,
                    DES_DECRYPT);
            else
                cbc_encrypt((des_cblock *)net,
                    (des_cblock *)buf,num,sched,iv,
                    DES_DECRYPT);
            }
        }
    return(num);
    }