Fixed PKCS5_PBKDF2_HMAC() to adhere to the documentation.

The documentation of this function states that the password parameter
can be NULL. However, the implementation returns an error in this case
due to the inner workings of the HMAC_Init_ex() function.
With this change, NULL password will be treated as an empty string and
PKCS5_PBKDF2_HMAC() no longer fails on this input.

I have also added two new test cases that tests the handling of the
special values NULL and -1 of the password and passlen parameters,
respectively.

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/1692)

crypto/evp/p5_crpt2.c

@@ -33,6 +33,7 @@ int PKCS5_PBKDF2_HMAC(const char *pass, int passlen,
                       const unsigned char *salt, int saltlen, int iter,
                       const EVP_MD *digest, int keylen, unsigned char *out)
 {
+    const char *empty = "";
     unsigned char digtmp[EVP_MAX_MD_SIZE], *p, itmp[4];
     int cplen, j, k, tkeylen, mdlen;
     unsigned long i = 1;
@@ -47,10 +48,12 @@ int PKCS5_PBKDF2_HMAC(const char *pass, int passlen,
         return 0;
     p = out;
     tkeylen = keylen;
-    if (!pass)
+    if (pass == NULL) {
+        pass = empty;
         passlen = 0;
-    else if (passlen == -1)
+    } else if (passlen == -1) {
         passlen = strlen(pass);
+    }
     if (!HMAC_Init_ex(hctx_tpl, pass, passlen, digest, NULL)) {
         HMAC_CTX_free(hctx_tpl);
         return 0;

test/evp_test.c

@@ -127,6 +127,8 @@ static int test_bin(const char *value, unsigned char **buf, size_t *buflen)
     long len;
 
     *buflen = 0;
+
+    /* Check for empty value */
     if (!*value) {
         /*
          * Don't return NULL for zero length buffer.
@@ -141,6 +143,14 @@ static int test_bin(const char *value, unsigned char **buf, size_t *buflen)
         *buflen = 0;
         return 1;
     }
+
+    /* Check for NULL literal */
+    if (strcmp(value, "NULL") == 0) {
+        *buf = NULL;
+        *buflen = 0;
+        return 1;
+    }
+
     /* Check for string literal */
     if (value[0] == '"') {
         size_t vlen;
@@ -155,6 +165,7 @@ static int test_bin(const char *value, unsigned char **buf, size_t *buflen)
         return 1;
     }
 
+    /* Otherwise assume as hex literal and convert it to binary buffer */
     *buf = OPENSSL_hexstr2buf(value, &len);
     if (!*buf) {
         fprintf(stderr, "Value=%s\n", value);
@@ -640,7 +651,7 @@ int main(int argc, char **argv)
 
     memset(&t, 0, sizeof(t));
     t.start_line = -1;
-    in = BIO_new_file(argv[1], "r");
+    in = BIO_new_file(argv[1], "rb");
     if (in == NULL) {
         fprintf(stderr, "Can't open %s for reading\n", argv[1]);
         return 1;

test/evptests.txt

@@ -3482,6 +3482,49 @@ iter = 4096
 MD = sha512
 Key = 9d9e9c4cd21fe4be24d5b8244c759665
 
+# PBKDF2 tests for empty and NULL inputs
+PBE = pbkdf2
+Password = ""
+Salt = "salt"
+iter = 1
+MD = sha1
+Key = a33dddc30478185515311f8752895d36ea4363a2
+
+PBE = pbkdf2
+Password = ""
+Salt = "salt"
+iter = 1
+MD = sha256
+Key = f135c27993baf98773c5cdb40a5706ce6a345cde
+
+PBE = pbkdf2
+Password = ""
+Salt = "salt"
+iter = 1
+MD = sha512
+Key = 00ef42cdbfc98d29db20976608e455567fdddf14
+
+PBE = pbkdf2
+Password = NULL
+Salt = "salt"
+iter = 1
+MD = sha1
+Key = a33dddc30478185515311f8752895d36ea4363a2
+
+PBE = pbkdf2
+Password = NULL
+Salt = "salt"
+iter = 1
+MD = sha256
+Key = f135c27993baf98773c5cdb40a5706ce6a345cde
+
+PBE = pbkdf2
+Password = NULL
+Salt = "salt"
+iter = 1
+MD = sha512
+Key = 00ef42cdbfc98d29db20976608e455567fdddf14
+
 # Base64 tests
 
 Encoding = canonical