Merge changes I1a855726,Ib7976671,I76e5ee5a into main
* changes:
keystore: remove misleading error message from AES_gcm_decrypt()
keystore: eliminate redundant key stretching
keystore: rename the PBKDF2 functions
diff --git a/keystore2/src/crypto/Android.bp b/keystore2/src/crypto/Android.bp
index 35fc5a9..c78ae41 100644
--- a/keystore2/src/crypto/Android.bp
+++ b/keystore2/src/crypto/Android.bp
@@ -74,7 +74,7 @@
"--allowlist-function", "AES_gcm_encrypt",
"--allowlist-function", "AES_gcm_decrypt",
"--allowlist-function", "CreateKeyId",
- "--allowlist-function", "generateKeyFromPassword",
+ "--allowlist-function", "PBKDF2",
"--allowlist-function", "HKDFExtract",
"--allowlist-function", "HKDFExpand",
"--allowlist-function", "ECDHComputeKey",
diff --git a/keystore2/src/crypto/crypto.cpp b/keystore2/src/crypto/crypto.cpp
index 7feeaff..56d8de6 100644
--- a/keystore2/src/crypto/crypto.cpp
+++ b/keystore2/src/crypto/crypto.cpp
@@ -141,7 +141,8 @@
EVP_DecryptUpdate(ctx.get(), out_pos, &out_len, in, len);
out_pos += out_len;
if (!EVP_DecryptFinal_ex(ctx.get(), out_pos, &out_len)) {
- ALOGE("Failed to decrypt blob; ciphertext or tag is likely corrupted");
+ // No error log here; this is expected when trying two different keys to see which one
+ // works. The callers handle the error appropriately.
return false;
}
out_pos += out_len;
@@ -191,8 +192,7 @@
// Copied from system/security/keystore/user_state.cpp.
-void generateKeyFromPassword(uint8_t* key, size_t key_len, const char* pw, size_t pw_len,
- const uint8_t* salt) {
+void PBKDF2(uint8_t* key, size_t key_len, const char* pw, size_t pw_len, const uint8_t* salt) {
const EVP_MD* digest = EVP_sha256();
// SHA1 was used prior to increasing the key size
diff --git a/keystore2/src/crypto/crypto.hpp b/keystore2/src/crypto/crypto.hpp
index 4a161e6..f67f640 100644
--- a/keystore2/src/crypto/crypto.hpp
+++ b/keystore2/src/crypto/crypto.hpp
@@ -37,8 +37,7 @@
bool CreateKeyId(const uint8_t* key_blob, size_t len, km_id_t* out_id);
// The salt parameter must be non-nullptr and point to 16 bytes of data.
- void generateKeyFromPassword(uint8_t* key, size_t key_len, const char* pw,
- size_t pw_len, const uint8_t* salt);
+ void PBKDF2(uint8_t* key, size_t key_len, const char* pw, size_t pw_len, const uint8_t* salt);
#include "openssl/digest.h"
#include "openssl/ec_key.h"
diff --git a/keystore2/src/crypto/lib.rs b/keystore2/src/crypto/lib.rs
index 8434651..09b84ec 100644
--- a/keystore2/src/crypto/lib.rs
+++ b/keystore2/src/crypto/lib.rs
@@ -19,10 +19,10 @@
pub mod zvec;
pub use error::Error;
use keystore2_crypto_bindgen::{
- extractSubjectFromCertificate, generateKeyFromPassword, hmacSha256, randomBytes,
- AES_gcm_decrypt, AES_gcm_encrypt, ECDHComputeKey, ECKEYGenerateKey, ECKEYMarshalPrivateKey,
- ECKEYParsePrivateKey, ECPOINTOct2Point, ECPOINTPoint2Oct, EC_KEY_free, EC_KEY_get0_public_key,
- EC_POINT_free, HKDFExpand, HKDFExtract, EC_KEY, EC_MAX_BYTES, EC_POINT, EVP_MAX_MD_SIZE,
+ extractSubjectFromCertificate, hmacSha256, randomBytes, AES_gcm_decrypt, AES_gcm_encrypt,
+ ECDHComputeKey, ECKEYGenerateKey, ECKEYMarshalPrivateKey, ECKEYParsePrivateKey,
+ ECPOINTOct2Point, ECPOINTPoint2Oct, EC_KEY_free, EC_KEY_get0_public_key, EC_POINT_free,
+ HKDFExpand, HKDFExtract, EC_KEY, EC_MAX_BYTES, EC_POINT, EVP_MAX_MD_SIZE, PBKDF2,
};
use std::convert::TryFrom;
use std::convert::TryInto;
@@ -172,7 +172,7 @@
}
}
-/// Represents a "password" that can be used to key the PBKDF2 algorithm.
+/// A high-entropy synthetic password from which an AES key may be derived.
pub enum Password<'a> {
/// Borrow an existing byte array
Ref(&'a [u8]),
@@ -194,25 +194,28 @@
}
}
- /// Generate a key from the given password and salt.
- /// The salt must be exactly 16 bytes long.
- /// Two key sizes are accepted: 16 and 32 bytes.
- pub fn derive_key(&self, salt: &[u8], key_length: usize) -> Result<ZVec, Error> {
+ /// Derives a key from the given password and salt, using PBKDF2 with 8192 iterations.
+ ///
+ /// The salt length must be 16 bytes, and the output key length must be 16 or 32 bytes.
+ ///
+ /// This function exists only for backwards compatibility reasons. Keystore now receives only
+ /// high-entropy synthetic passwords, which do not require key stretching.
+ pub fn derive_key_pbkdf2(&self, salt: &[u8], out_len: usize) -> Result<ZVec, Error> {
if salt.len() != SALT_LENGTH {
return Err(Error::InvalidSaltLength);
}
- match key_length {
+ match out_len {
AES_128_KEY_LENGTH | AES_256_KEY_LENGTH => {}
_ => return Err(Error::InvalidKeyLength),
}
let pw = self.get_key();
- let mut result = ZVec::new(key_length)?;
+ let mut result = ZVec::new(out_len)?;
// Safety: We checked that the salt is exactly 16 bytes long. The other pointers are valid,
// and have matching lengths.
unsafe {
- generateKeyFromPassword(
+ PBKDF2(
result.as_mut_ptr(),
result.len(),
pw.as_ptr() as *const std::os::raw::c_char,
@@ -224,6 +227,13 @@
Ok(result)
}
+ /// Derives a key from the given high-entropy synthetic password and salt, using HKDF.
+ pub fn derive_key_hkdf(&self, salt: &[u8], out_len: usize) -> Result<ZVec, Error> {
+ let prk = hkdf_extract(self.get_key(), salt)?;
+ let info = [];
+ hkdf_expand(out_len, &prk, &info)
+ }
+
/// Try to make another Password object with the same data.
pub fn try_clone(&self) -> Result<Password<'static>, Error> {
Ok(Password::Owned(ZVec::try_from(self.get_key())?))
@@ -471,9 +481,7 @@
mod tests {
use super::*;
- use keystore2_crypto_bindgen::{
- generateKeyFromPassword, AES_gcm_decrypt, AES_gcm_encrypt, CreateKeyId,
- };
+ use keystore2_crypto_bindgen::{AES_gcm_decrypt, AES_gcm_encrypt, CreateKeyId, PBKDF2};
#[test]
fn test_wrapper_roundtrip() {
@@ -535,21 +543,15 @@
}
#[test]
- fn test_generate_key_from_password() {
+ fn test_pbkdf2() {
let mut key = vec![0; 16];
let pw = [0; 16];
let salt = [0; 16];
// SAFETY: The pointers are obtained from references so they are valid, the salt is the
- // expected length, the other lengths match the lengths of the arrays, and
- // `generateKeyFromPassword` doesn't access them after it returns.
+ // expected length, the other lengths match the lengths of the arrays, and `PBKDF2` doesn't
+ // access them after it returns.
unsafe {
- generateKeyFromPassword(
- key.as_mut_ptr(),
- key.len(),
- pw.as_ptr(),
- pw.len(),
- salt.as_ptr(),
- );
+ PBKDF2(key.as_mut_ptr(), key.len(), pw.as_ptr(), pw.len(), salt.as_ptr());
}
assert_ne!(key, vec![0; 16]);
}
diff --git a/keystore2/src/fuzzers/keystore2_unsafe_fuzzer.rs b/keystore2/src/fuzzers/keystore2_unsafe_fuzzer.rs
index 8b8843d..fb4c9ad 100644
--- a/keystore2/src/fuzzers/keystore2_unsafe_fuzzer.rs
+++ b/keystore2/src/fuzzers/keystore2_unsafe_fuzzer.rs
@@ -144,7 +144,8 @@
let _res = aes_gcm_encrypt(plaintext, key_aes_encrypt);
}
FuzzCommand::Password { pw, salt, key_length } => {
- let _res = Password::from(pw).derive_key(salt, key_length % MAX_SIZE_MODIFIER);
+ let _res =
+ Password::from(pw).derive_key_pbkdf2(salt, key_length % MAX_SIZE_MODIFIER);
}
FuzzCommand::HkdfExtract { hkdf_secret, hkdf_salt } => {
let _res = hkdf_extract(hkdf_secret, hkdf_salt);
diff --git a/keystore2/src/legacy_blob.rs b/keystore2/src/legacy_blob.rs
index 2ffcc71..2bb7f27 100644
--- a/keystore2/src/legacy_blob.rs
+++ b/keystore2/src/legacy_blob.rs
@@ -1313,7 +1313,7 @@
Blob { flags, value: BlobValue::PwEncrypted { iv, tag, data, salt, key_size } } => {
if (flags & flags::ENCRYPTED) != 0 {
let key = pw
- .derive_key(&salt, key_size)
+ .derive_key_pbkdf2(&salt, key_size)
.context(ks_err!("Failed to derive key from password."))?;
let blob = aes_gcm_decrypt(&data, &iv, &tag, &key)
.context(ks_err!("while trying to decrypt legacy super key blob."))?;
@@ -1953,7 +1953,7 @@
std::fs::create_dir(&*temp_dir.build().push("user_0")).unwrap();
let pw: Password = PASSWORD.into();
- let pw_key = TestKey(pw.derive_key(SUPERKEY_SALT, 32).unwrap());
+ let pw_key = TestKey(pw.derive_key_pbkdf2(SUPERKEY_SALT, 32).unwrap());
let super_key =
Arc::new(TestKey(pw_key.decrypt(SUPERKEY_PAYLOAD, SUPERKEY_IV, SUPERKEY_TAG).unwrap()));
@@ -2040,7 +2040,7 @@
std::fs::create_dir(&*temp_dir.build().push("user_0")).unwrap();
let pw: Password = PASSWORD.into();
- let pw_key = TestKey(pw.derive_key(SUPERKEY_SALT, 32).unwrap());
+ let pw_key = TestKey(pw.derive_key_pbkdf2(SUPERKEY_SALT, 32).unwrap());
let super_key =
Arc::new(TestKey(pw_key.decrypt(SUPERKEY_PAYLOAD, SUPERKEY_IV, SUPERKEY_TAG).unwrap()));
@@ -2128,7 +2128,7 @@
std::fs::create_dir(&*temp_dir.build().push("user_0")).unwrap();
let pw: Password = PASSWORD.into();
- let pw_key = TestKey(pw.derive_key(SUPERKEY_SALT, 32).unwrap());
+ let pw_key = TestKey(pw.derive_key_pbkdf2(SUPERKEY_SALT, 32).unwrap());
let super_key =
Arc::new(TestKey(pw_key.decrypt(SUPERKEY_PAYLOAD, SUPERKEY_IV, SUPERKEY_TAG).unwrap()));
diff --git a/keystore2/src/super_key.rs b/keystore2/src/super_key.rs
index 3992eb2..9c17ccb 100644
--- a/keystore2/src/super_key.rs
+++ b/keystore2/src/super_key.rs
@@ -532,11 +532,17 @@
(Some(&EncryptedBy::Password), Some(salt), Some(iv), Some(tag)) => {
// Note that password encryption is AES no matter the value of algorithm.
let key = pw
- .derive_key(salt, AES_256_KEY_LENGTH)
- .context(ks_err!("Failed to generate key from password."))?;
+ .derive_key_hkdf(salt, AES_256_KEY_LENGTH)
+ .context(ks_err!("Failed to derive key from password."))?;
- aes_gcm_decrypt(blob, iv, tag, &key)
- .context(ks_err!("Failed to decrypt key blob."))?
+ aes_gcm_decrypt(blob, iv, tag, &key).or_else(|_e| {
+ // Handle old key stored before the switch to HKDF.
+ let key = pw
+ .derive_key_pbkdf2(salt, AES_256_KEY_LENGTH)
+ .context(ks_err!("Failed to derive key from password (PBKDF2)."))?;
+ aes_gcm_decrypt(blob, iv, tag, &key)
+ .context(ks_err!("Failed to decrypt key blob."))
+ })?
}
(enc_by, salt, iv, tag) => {
return Err(Error::Rc(ResponseCode::VALUE_CORRUPTED)).context(ks_err!(
@@ -563,14 +569,20 @@
}
/// Encrypts the super key from a key derived from the password, before storing in the database.
+ /// This does not stretch the password; i.e., it assumes that the password is a high-entropy
+ /// synthetic password, not a low-entropy user provided password.
pub fn encrypt_with_password(
super_key: &[u8],
pw: &Password,
) -> Result<(Vec<u8>, BlobMetaData)> {
let salt = generate_salt().context("In encrypt_with_password: Failed to generate salt.")?;
- let derived_key = pw
- .derive_key(&salt, AES_256_KEY_LENGTH)
- .context(ks_err!("Failed to derive password."))?;
+ let derived_key = if android_security_flags::fix_unlocked_device_required_keys_v2() {
+ pw.derive_key_hkdf(&salt, AES_256_KEY_LENGTH)
+ .context(ks_err!("Failed to derive key from password."))?
+ } else {
+ pw.derive_key_pbkdf2(&salt, AES_256_KEY_LENGTH)
+ .context(ks_err!("Failed to derive password."))?
+ };
let mut metadata = BlobMetaData::new();
metadata.add(BlobMetaEntry::EncryptedBy(EncryptedBy::Password));
metadata.add(BlobMetaEntry::Salt(salt));
diff --git a/keystore2/tests/legacy_blobs/keystore2_legacy_blob_tests.rs b/keystore2/tests/legacy_blobs/keystore2_legacy_blob_tests.rs
index c2cd3ad..0335159 100644
--- a/keystore2/tests/legacy_blobs/keystore2_legacy_blob_tests.rs
+++ b/keystore2/tests/legacy_blobs/keystore2_legacy_blob_tests.rs
@@ -174,7 +174,7 @@
// Create keystore file layout for user_99.
let pw: Password = PASSWORD.into();
- let pw_key = TestKey(pw.derive_key(SUPERKEY_SALT, 32).unwrap());
+ let pw_key = TestKey(pw.derive_key_pbkdf2(SUPERKEY_SALT, 32).unwrap());
let super_key =
TestKey(pw_key.decrypt(SUPERKEY_PAYLOAD, SUPERKEY_IV, SUPERKEY_TAG).unwrap());
@@ -427,7 +427,7 @@
// Create keystore file layout for user_98.
let pw: Password = PASSWORD.into();
- let pw_key = TestKey(pw.derive_key(SUPERKEY_SALT, 32).unwrap());
+ let pw_key = TestKey(pw.derive_key_pbkdf2(SUPERKEY_SALT, 32).unwrap());
let super_key =
TestKey(pw_key.decrypt(SUPERKEY_PAYLOAD, SUPERKEY_IV, SUPERKEY_TAG).unwrap());