crypto/symmetrickey: remove most remaining methods

This change removes:
* DeriveKeyFromPasswordUsingPbkdf2
* ImportKey
* HMAC-SHA1 key support generically
* Test coverage for the above

There are two remaining clients of random AES key generation to remove,
then SymmetricKey itself will go away. :)

Bug: 370724578
Change-Id: I802ab5301c8038de7b3f8cd18aedcbb6d19ec044
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6289025
Commit-Queue: Elly FJ <ellyjones@chromium.org>
Reviewed-by: David Benjamin <davidben@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1424114}

crypto/symmetric_key.cc

@@ -10,9 +10,6 @@
 #include <algorithm>
 #include <utility>
 
-#include "base/check_op.h"
-#include "base/notreached.h"
-#include "crypto/kdf.h"
 #include "crypto/openssl_util.h"
 #include "crypto/random.h"
 
@@ -55,28 +52,6 @@ SymmetricKey SymmetricKey::RandomKey(size_t key_size_in_bits) {
   return SymmetricKey(crypto::RandBytesAsVector(key_size_in_bytes));
 }
 
-// static
-std::unique_ptr<SymmetricKey> SymmetricKey::DeriveKeyFromPasswordUsingPbkdf2(
-    Algorithm,
-    const std::string& password,
-    const std::string& salt,
-    size_t iterations,
-    size_t key_size_in_bits) {
-  if ((key_size_in_bits % 8) || !IsValidKeySize(key_size_in_bits / 8)) {
-    return nullptr;
-  }
-
-  kdf::Pbkdf2HmacSha1Params params = {
-      .iterations = base::checked_cast<decltype(params.iterations)>(iterations),
-  };
-
-  std::vector<uint8_t> key(key_size_in_bits / 8);
-  kdf::DeriveKeyPbkdf2HmacSha1(params, base::as_byte_span(password),
-                               base::as_byte_span(salt), key, SubtlePassKey{});
-
-  return std::make_unique<SymmetricKey>(key);
-}
-
 // static
 std::unique_ptr<SymmetricKey> SymmetricKey::Import(Algorithm,
                                                    const std::string& raw_key) {

crypto/symmetric_key.h

@@ -17,7 +17,7 @@
 namespace crypto {
 
 // A SymmetricKey is an array of bytes which is used for symmetric cryptography
-// (encryption or MACs).
+// (encryption only).
 //
 // This whole type is deprecated: prefer to use raw std::array<uint8_t>,
 // std::vector<uint8_t>, or base::span<uint8_t> instead. This type has no
@@ -30,7 +30,6 @@ class CRYPTO_EXPORT SymmetricKey {
   // class Encryptor.
   enum Algorithm {
     AES,
-    HMAC_SHA1,
   };
 
   SymmetricKey() = delete;
@@ -52,24 +51,10 @@ class CRYPTO_EXPORT SymmetricKey {
 
   static SymmetricKey RandomKey(size_t key_size_in_bits);
 
-  // Derives a key from the supplied password and salt using PBKDF2, suitable
-  // for use with specified |algorithm|. Note |algorithm| is not the algorithm
-  // used to derive the key from the password. |key_size_in_bits| must be a
-  // multiple of 8. The caller is responsible for deleting the returned
-  // SymmetricKey.
-  //
-  // Deprecated: use crypto::kdf::DeriveKeyPbkdf2HmacSha1() instead.
-  static std::unique_ptr<SymmetricKey> DeriveKeyFromPasswordUsingPbkdf2(
-      Algorithm algorithm,
-      const std::string& password,
-      const std::string& salt,
-      size_t iterations,
-      size_t key_size_in_bits);
-
-  // Imports an array of key bytes in |raw_key|. This key may have been
-  // generated by GenerateRandomKey or DeriveKeyFromPassword{Pbkdf2,Scrypt} and
-  // exported with key(). The key must be of suitable size for use with
-  // |algorithm|. The caller owns the returned SymmetricKey.
+  // Imports an array of key bytes in |raw_key|. The raw key must be of a valid
+  // size - see IsValidKeySize() in the source for details, although in general
+  // you should not need to choose key sizes yourself. Returns nullptr if the
+  // key is not of valid size.
   //
   // Deprecated: use the regular constructor that accepts a span of bytes, and
   // validate that the key is of whatever length your client code expects before
@@ -77,7 +62,7 @@ class CRYPTO_EXPORT SymmetricKey {
   static std::unique_ptr<SymmetricKey> Import(Algorithm algorithm,
                                               const std::string& raw_key);
 
-  // Returns the raw platform specific key data.
+  // Returns the internal key storage.
   const std::string& key() const { return key_; }
 
  private:

crypto/symmetric_key_unittest.cc

@@ -37,16 +37,3 @@ TEST(SymmetricKeyTest, ImportGeneratedKey) {
 
   EXPECT_EQ(key1->key(), key2->key());
 }
-
-TEST(SymmetricKeyTest, ImportDerivedKey) {
-  std::unique_ptr<crypto::SymmetricKey> key1(
-      crypto::SymmetricKey::DeriveKeyFromPasswordUsingPbkdf2(
-          crypto::SymmetricKey::HMAC_SHA1, "password", "somesalt", 1024, 128));
-  ASSERT_TRUE(key1);
-
-  std::unique_ptr<crypto::SymmetricKey> key2(crypto::SymmetricKey::Import(
-      crypto::SymmetricKey::HMAC_SHA1, key1->key()));
-  ASSERT_TRUE(key2);
-
-  EXPECT_EQ(key1->key(), key2->key());
-}