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enchive
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Tweak MAC.

pull/2/head
Christopher Wellons 2017-03-03 16:15:09 -05:00
parent 0ca842f188
commit dbef75e106
3 changed files with 24 additions and 17 deletions
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4
README.md
View File

@ -49,7 +49,7 @@ The process for encrypting a file:
4. Write the 8-byte IV.
5. Write the 32-byte ephemeral public key.
6. Encrypt the file with ChaCha20 and write the ciphertext.
7. Write the SHA-224 hash of IV+plaintext.
7. Write `sha256(key + sha256(plaintext))`.
The process for decrypting a file:
@ -59,4 +59,4 @@ The process for decrypting a file:
public key.
4. Initialize ChaCha20 with the shared secret as the key.
5. Decrypt the ciphertext using ChaCha20.
6. Verify the SHA-224 hash of IV+plaintext at the end of the file.
6. Verify `sha256(key + sha256(plaintext))`.

36
enchive.c
View File

@ -64,13 +64,12 @@ static void
symmetric_encrypt(FILE *in, FILE *out, u8 *key, u8 *iv)
{
static u8 buffer[2][CHACHA_BLOCKLENGTH * 1024];
u8 sha256[SHA256_BLOCK_SIZE];
u8 msghash[SHA256_BLOCK_SIZE];
SHA256_CTX hash[1];
chacha_ctx ctx[1];
chacha_keysetup(ctx, key, 256);
chacha_ivsetup(ctx, iv);
sha256_init(hash);
sha256_update(hash, iv, 8);
for (;;) {
size_t z = fread(buffer[0], 1, sizeof(buffer[0]), in);
@ -87,8 +86,13 @@ symmetric_encrypt(FILE *in, FILE *out, u8 *key, u8 *iv)
break;
}
sha256_final(hash, sha256);
if (!fwrite(sha256, SHA224_BLOCK_SIZE, 1, out))
sha256_final(hash, msghash);
sha256_init(hash);
sha256_update(hash, key, 32);
sha256_update(hash, msghash, sizeof(msghash));
sha256_final(hash, msghash);
if (!fwrite(msghash, SHA256_BLOCK_SIZE, 1, out))
fatal("error writing checksum to ciphertext file");
if (fflush(out))
fatal("error flushing to ciphertext file");
@ -97,17 +101,16 @@ symmetric_encrypt(FILE *in, FILE *out, u8 *key, u8 *iv)
static void
symmetric_decrypt(FILE *in, FILE *out, u8 *key, u8 *iv)
{
static u8 buffer[2][CHACHA_BLOCKLENGTH * 1024 + SHA224_BLOCK_SIZE];
u8 sha256[SHA256_BLOCK_SIZE];
static u8 buffer[2][CHACHA_BLOCKLENGTH * 1024 + SHA256_BLOCK_SIZE];
u8 msghash[SHA256_BLOCK_SIZE];
SHA256_CTX hash[1];
chacha_ctx ctx[1];
chacha_keysetup(ctx, key, 256);
chacha_ivsetup(ctx, iv);
sha256_init(hash);
sha256_update(hash, iv, 8);
/* Always keep SHA224_BLOCK_SIZE bytes in the buffer. */
if (!(fread(buffer[0], SHA224_BLOCK_SIZE, 1, in))) {
if (!(fread(buffer[0], SHA256_BLOCK_SIZE, 1, in))) {
if (ferror(in))
fatal("cannot read ciphertext file");
else
@ -115,8 +118,8 @@ symmetric_decrypt(FILE *in, FILE *out, u8 *key, u8 *iv)
}
for (;;) {
u8 *p = buffer[0] + SHA224_BLOCK_SIZE;
size_t z = fread(p, 1, sizeof(buffer[0]) - SHA224_BLOCK_SIZE, in);
u8 *p = buffer[0] + SHA256_BLOCK_SIZE;
size_t z = fread(p, 1, sizeof(buffer[0]) - SHA256_BLOCK_SIZE, in);
if (!z) {
if (ferror(in))
fatal("error reading ciphertext file");
@ -128,14 +131,19 @@ symmetric_decrypt(FILE *in, FILE *out, u8 *key, u8 *iv)
fatal("error writing plaintext file");
/* Move last SHA224_BLOCK_SIZE bytes to the front. */
memmove(buffer[0], buffer[0] + z, SHA224_BLOCK_SIZE);
memmove(buffer[0], buffer[0] + z, SHA256_BLOCK_SIZE);
if (z < sizeof(buffer[0]) - SHA224_BLOCK_SIZE)
if (z < sizeof(buffer[0]) - SHA256_BLOCK_SIZE)
break;
}
sha256_final(hash, sha256);
if (memcmp(buffer[0], sha256, SHA224_BLOCK_SIZE) != 0)
sha256_final(hash, msghash);
sha256_init(hash);
sha256_update(hash, key, 32);
sha256_update(hash, msghash, sizeof(msghash));
sha256_final(hash, msghash);
if (memcmp(buffer[0], msghash, SHA256_BLOCK_SIZE) != 0)
fatal("checksum mismatch!");
if (fflush(out))
fatal("error flushing to plaintext file");

1
sha256.h
View File

@ -12,7 +12,6 @@
#include <stddef.h>
#include "machine.h"
#define SHA224_BLOCK_SIZE 28
#define SHA256_BLOCK_SIZE 32
typedef unsigned char BYTE;