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/*
encrypt file by writing
v2hdr,
16byte initialization vector,
AES-CBC(key, random | file),
HMAC_SHA1(md5(key), AES-CBC(random | file))
*/
#include <u.h>
#include <libc.h>
#include <bio.h>
#include <mp.h>
#include <libsec.h>
extern char* getpassm(char*);
enum{ CHK = 16, BUF = 4096 };
uchar v2hdr[AESbsize+1] = "AES CBC SHA1 2\n";
Biobuf bin;
Biobuf bout;
void
safewrite(uchar *buf, int n)
{
int i = Bwrite(&bout, buf, n);
if(i == n)
return;
fprint(2, "write error\n");
exits("write error");
}
void
saferead(uchar *buf, int n)
{
int i = Bread(&bin, buf, n);
if(i == n)
return;
fprint(2, "read error\n");
exits("read error");
}
uchar *copy;
int ncopy;
void
safecopy(uchar *buf, int n)
{
copy = realloc(copy, ncopy+n);
if(copy == nil) {
fprint(2, "out of memory\n");
exits("memory");
}
memmove(copy+ncopy, buf, n);
ncopy += n;
}
int
main(int argc, char **argv)
{
int encrypt = 0; /* 0=decrypt, 1=encrypt */
int n, nkey, pass_stdin = 0;
char *pass;
uchar key[AESmaxkey], key2[SHA1dlen];
uchar buf[BUF+SHA1dlen]; /* assumption: CHK <= SHA1dlen */
AESstate aes;
DigestState *dstate;
ARGBEGIN{
case 'e':
encrypt = 1;
break;
case 'i':
pass_stdin = 1;
break;
}ARGEND;
if(argc!=0){
fprint(2,"usage: %s -d < cipher.aes > clear.txt\n", argv0);
fprint(2," or: %s -e < clear.txt > cipher.aes\n", argv0);
exits("usage");
}
Binit(&bin, 0, OREAD);
Binit(&bout, 1, OWRITE);
if(pass_stdin){
n = readn(3, buf, (sizeof buf)-1);
if(n < 1)
exits("usage: echo password |[3=1] auth/aescbc -i ...");
buf[n] = 0;
while(buf[n-1] == '\n')
buf[--n] = 0;
}else{
pass = readcons("aescbc password", nil, 1);
if(pass == nil)
exits("readcons");
n = strlen(pass);
if(n >= BUF)
exits("key too long");
strcpy((char*)buf, pass);
memset(pass, 0, n);
free(pass);
}
if(n <= 0){
fprint(2,"no key\n");
exits("key");
}
dstate = sha1((uchar*)"aescbc file", 11, nil, nil);
sha1(buf, n, key2, dstate);
memcpy(key, key2, 16);
nkey = 16;
md5(key, nkey, key2, 0); /* so even if HMAC_SHA1 is broken, encryption key is protected */
if(encrypt){
safewrite(v2hdr, AESbsize);
genrandom(buf,2*AESbsize); /* CBC is semantically secure if IV is unpredictable. */
setupAESstate(&aes, key, nkey, buf); /* use first AESbsize bytes as IV */
aesCBCencrypt(buf+AESbsize, AESbsize, &aes); /* use second AESbsize bytes as initial plaintext */
safewrite(buf, 2*AESbsize);
dstate = hmac_sha1(buf+AESbsize, AESbsize, key2, MD5dlen, 0, 0);
for(;;){
n = Bread(&bin, buf, BUF);
if(n < 0){
fprint(2,"read error\n");
exits("read error");
}
aesCBCencrypt(buf, n, &aes);
safewrite(buf, n);
dstate = hmac_sha1(buf, n, key2, MD5dlen, 0, dstate);
if(n < BUF)
break; /* EOF */
}
hmac_sha1(0, 0, key2, MD5dlen, buf, dstate);
safewrite(buf, SHA1dlen);
}else{ /* decrypt */
saferead(buf, AESbsize);
if(memcmp(buf, v2hdr, AESbsize) != 0){
fprint(2, "not an aescbc file\n");
exits("aescbc file");
}
saferead(buf, 2*AESbsize); /* read IV and random initial plaintext */
setupAESstate(&aes, key, nkey, buf);
dstate = hmac_sha1(buf+AESbsize, AESbsize, key2, MD5dlen, 0, 0);
aesCBCdecrypt(buf+AESbsize, AESbsize, &aes);
saferead(buf, SHA1dlen);
while((n = Bread(&bin, buf+SHA1dlen, BUF)) > 0){
dstate = hmac_sha1(buf, n, key2, MD5dlen, 0, dstate);
aesCBCdecrypt(buf, n, &aes);
safecopy(buf, n);
memmove(buf, buf+n, SHA1dlen); /* these bytes are not yet decrypted */
}
hmac_sha1(0, 0, key2, MD5dlen, buf+SHA1dlen, dstate);
if(memcmp(buf, buf+SHA1dlen, SHA1dlen) != 0){
fprint(2,"decrypted file failed to authenticate\n");
exits("decrypted file failed to authenticate");
}
safewrite(copy, ncopy);
}
exits("");
return 1; /* gcc */
}
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