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Remove extra passphrase mixing from key derivation.

pull/2/head
Christopher Wellons 2017-03-08 10:07:29 -05:00
parent 65467d2fe3
commit ff6ac9c7ca
2 changed files with 6 additions and 14 deletions
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15
README.md
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@ -124,20 +124,15 @@ of memory (D=29) by default, and protection key derivation requires
2. Compute `HMAC_SHA256(salt, passphrase)` and write this 32-byte
result to the beginning of *M*.
3. For each uninitialized 32-byte chunk in *M*, compute the SHA-256
hash of the previous 32-byte chunk concatenated with the
passphrase.
hash of the previous 32-byte chunk.
4. Initialize a byte pointer *P* to the last 32-byte chunk of *M*.
5. Compute the SHA-256 of the 32 bytes at *P* concatenated with the
passphrase.
6. Overwrite the memory at *P* with this new hash value.
7. Take the first *D* bits of this hash and use this value to set a
new *P* pointing elsewhere into *M*.
5. Compute the SHA-256 hash, *H*, of the 32 bytes at *P*.
6. Overwrite the memory at *P* with *H*.
7. Take the first *D* bits of *H* and use this value to set a new *P*
pointing into *M*.
8. Repeat from step 5 `1 << (D - 5)` times.
9. *P* points to the result.
The passphrase is always concatenated on the end so that the hash
context can't be precomputed.
## Compilation
To build on any unix-like system, run `make`. The resulting binary has

5
src/enchive.c
View File

@ -374,7 +374,6 @@ static void
key_derive(const char *passphrase, u8 *buf, int iexp, const u8 *salt)
{
static const u8 empty[8] = {0};
size_t len = strlen(passphrase);
SHA256_CTX ctx[1];
unsigned long i;
unsigned long memlen = 1UL << iexp;
@ -389,7 +388,7 @@ key_derive(const char *passphrase, u8 *buf, int iexp, const u8 *salt)
if (!salt)
salt = empty;
hmac_init(ctx, salt);
sha256_update(ctx, (u8 *)passphrase, len);
sha256_update(ctx, (u8 *)passphrase, strlen(passphrase));
hmac_final(ctx, salt, memory);
for (p = memory + SHA256_BLOCK_SIZE;
@ -397,7 +396,6 @@ key_derive(const char *passphrase, u8 *buf, int iexp, const u8 *salt)
p += SHA256_BLOCK_SIZE) {
sha256_init(ctx);
sha256_update(ctx, p - SHA256_BLOCK_SIZE, SHA256_BLOCK_SIZE);
sha256_update(ctx, (u8 *)passphrase, len);
sha256_final(ctx, p);
}
@ -406,7 +404,6 @@ key_derive(const char *passphrase, u8 *buf, int iexp, const u8 *salt)
unsigned long offset;
sha256_init(ctx);
sha256_update(ctx, memptr, SHA256_BLOCK_SIZE);
sha256_update(ctx, (u8 *)passphrase, len);
sha256_final(ctx, memptr);
offset = ((unsigned long)memptr[3] << 24 |
(unsigned long)memptr[2] << 16 |