Hi,
I was reading over bf_key_init() in Vim's blowfish.c.
* sha256_key() finalises the "input" key to be used by blowfish
* sha256_key() is simply a wrapper for sha256_bytes()
* sha256_bytes() has a static buffer (hexit), which is the hex string
of the key it generates
* sha256_bytes() returns a pointer to hexit; after bf_key_init() uses
this data it is persisted in memory
* buffer hexit is local to sha256_bytes() so the only way to clear it
is to call the function again (without restructuring the code)
* sha256_bytes() also doesn't zero the binary value of the key (sha256sum)
or the sha256 context (ctx).
This patch adds a new function, sha256_poison(), to reset the variables
in sha256_bytes(). bf_key_init() uses this this after it finishes
building the blowfish key context.
While here, zero ctx & sha256sum in sha256_bytes().
- Michael
diff --git a/src/blowfish.c b/src/blowfish.c
index eaf0b9e..e145708 100644
--- a/src/blowfish.c
+++ b/src/blowfish.c
@@ -464,6 +464,8 @@ bf_key_init(
bfs->sbx[i][j + 1] = data_r;
}
}
+
+ sha256_poison();
}
/*
diff --git a/src/sha256.c b/src/sha256.c
index 3bb7791..6bc8ab7 100644
--- a/src/sha256.c
+++ b/src/sha256.c
@@ -293,6 +293,10 @@ sha256_bytes(
for (j = 0; j < 32; j++)
sprintf((char *)hexit + j * 2, "%02x", sha256sum[j]);
hexit[sizeof(hexit) - 1] = '\0';
+
+ vim_memset(sha256sum, 0, sizeof(sha256sum));
+ vim_memset(&ctx, 0, sizeof(ctx));
+
return hexit;
}
@@ -312,6 +316,13 @@ sha256_key(
return sha256_bytes(buf, (int)STRLEN(buf), salt, salt_len);
}
+void
+sha256_poison(void)
+{
+ char_u *buf = "...";
+ (void) sha256_bytes(buf, (int)STRLEN(buf), NULL, 0);
+}
+
/*
* These are the standard FIPS-180-2 test vectors
*/
--
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