CVE-2021-20251 lib:crypto: Add Python functions for AES SAMR password change

These functions allow us to perform key derivation and AES256 encryption
in Python. They will be used in a following commit.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=14611

Signed-off-by: Joseph Sutton <josephsutton@catalyst.net.nz>
Reviewed-by: Andreas Schneider <asn@samba.org>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>

1 files changed, 221 insertions, 0 deletions

diff --git a/lib/crypto/py_crypto.c b/lib/crypto/py_crypto.c
index 40b0cb9e9c0..11659556884 100644
--- a/lib/crypto/py_crypto.c
+++ b/lib/crypto/py_crypto.c
@@ -27,6 +27,51 @@
 #include "lib/crypto/gnutls_helpers.h"
 #include "lib/crypto/md4.h"
 #include "libcli/auth/libcli_auth.h"
+#include "libcli/util/pyerrors.h"
+
+#ifdef HAVE_GNUTLS_PBKDF2
+static bool samba_gnutls_datum_from_PyObject(PyObject *py_obj,
+					     gnutls_datum_t *datum)
+{
+	uint8_t *data = NULL;
+	Py_ssize_t size;
+
+	int ret;
+
+	ret = PyBytes_AsStringAndSize(py_obj,
+				      (char **)&data,
+				      &size);
+	if (ret != 0) {
+		return false;
+	}
+
+	datum->data = data;
+	datum->size = size;
+
+	return true;
+}
+#endif /* HAVE_GNUTLS_PBKDF2 */
+
+static bool samba_DATA_BLOB_from_PyObject(PyObject *py_obj,
+					  DATA_BLOB *blob)
+{
+	uint8_t *data = NULL;
+	Py_ssize_t size;
+
+	int ret;
+
+	ret = PyBytes_AsStringAndSize(py_obj,
+				      (char **)&data,
+				      &size);
+	if (ret != 0) {
+		return false;
+	}
+
+	blob->data = data;
+	blob->length = size;
+
+	return true;
+}
 
 static PyObject *py_crypto_arcfour_crypt_blob(PyObject *module, PyObject *args)
 {
@@ -191,6 +236,165 @@ static PyObject *py_crypto_md4_hash_blob(PyObject *self, PyObject *args)
 					 sizeof(result));
 }
 
+static PyObject *py_crypto_sha512_pbkdf2(PyObject *self, PyObject *args)
+{
+#ifdef HAVE_GNUTLS_PBKDF2
+	PyObject *py_key = NULL;
+	uint8_t *key = NULL;
+	gnutls_datum_t key_datum = {0};
+
+	PyObject *py_salt = NULL;
+	gnutls_datum_t salt_datum = {0};
+
+	uint8_t result[16];
+
+	unsigned iterations = 0;
+
+	bool ok;
+	int ret;
+	NTSTATUS status;
+
+	ok = PyArg_ParseTuple(args, "SSI",
+			      &py_key, &py_salt, &iterations);
+	if (!ok) {
+		return NULL;
+	}
+
+	ok = samba_gnutls_datum_from_PyObject(py_key, &key_datum);
+	if (!ok) {
+		return NULL;
+	}
+
+	ok = samba_gnutls_datum_from_PyObject(py_salt, &salt_datum);
+	if (!ok) {
+		return NULL;
+	}
+
+	ret = gnutls_pbkdf2(GNUTLS_MAC_SHA512,
+			    &key_datum,
+			    &salt_datum,
+			    iterations,
+			    result,
+			    sizeof(result));
+	BURN_DATA(key);
+	if (ret < 0) {
+		status = gnutls_error_to_ntstatus(ret, NT_STATUS_CRYPTO_SYSTEM_INVALID);
+		PyErr_SetNTSTATUS(status);
+		return NULL;
+	}
+
+	return PyBytes_FromStringAndSize((const char *)result,
+					 sizeof(result));
+#else /* HAVE_GNUTLS_PBKDF2 */
+	PyErr_SetString(PyExc_NotImplementedError, "gnutls_pbkdf2() is not available");
+	return NULL;
+#endif /* HAVE_GNUTLS_PBKDF2 */
+}
+
+static PyObject *py_crypto_aead_aes_256_cbc_hmac_sha512_blob(PyObject *self, PyObject *args)
+{
+	TALLOC_CTX *ctx = NULL;
+
+	PyObject *py_ciphertext = NULL;
+	DATA_BLOB ciphertext_blob = {0};
+
+	PyObject *py_auth_data = NULL;
+	PyObject *py_result = NULL;
+
+	PyObject *py_plaintext = NULL;
+	DATA_BLOB plaintext_blob = {0};
+	PyObject *py_cek = NULL;
+	DATA_BLOB cek_blob = {0};
+	PyObject *py_key_salt = NULL;
+	DATA_BLOB key_salt_blob = {0};
+	PyObject *py_mac_salt = NULL;
+	DATA_BLOB mac_salt_blob = {0};
+	PyObject *py_iv = NULL;
+	DATA_BLOB iv_blob = {0};
+
+	uint8_t auth_data[64];
+
+	bool ok;
+	NTSTATUS status;
+
+	ok = PyArg_ParseTuple(args, "SSSSS",
+			      &py_plaintext,
+			      &py_cek,
+			      &py_key_salt,
+			      &py_mac_salt,
+			      &py_iv);
+	if (!ok) {
+		return NULL;
+	}
+
+	/* Create data blobs from the contents of the function parameters. */
+
+	ok = samba_DATA_BLOB_from_PyObject(py_plaintext, &plaintext_blob);
+	if (!ok) {
+		return NULL;
+	}
+
+	ok = samba_DATA_BLOB_from_PyObject(py_cek, &cek_blob);
+	if (!ok) {
+		return NULL;
+	}
+
+	ok = samba_DATA_BLOB_from_PyObject(py_key_salt, &key_salt_blob);
+	if (!ok) {
+		return NULL;
+	}
+
+	ok = samba_DATA_BLOB_from_PyObject(py_mac_salt, &mac_salt_blob);
+	if (!ok) {
+		return NULL;
+	}
+
+	ok = samba_DATA_BLOB_from_PyObject(py_iv, &iv_blob);
+	if (!ok) {
+		return NULL;
+	}
+
+	ctx = talloc_new(NULL);
+	if (ctx == NULL) {
+		return PyErr_NoMemory();
+	}
+
+	/* Encrypt the plaintext. */
+	status = samba_gnutls_aead_aes_256_cbc_hmac_sha512_encrypt(ctx,
+								   &plaintext_blob,
+								   &cek_blob,
+								   &key_salt_blob,
+								   &mac_salt_blob,
+								   &iv_blob,
+								   &ciphertext_blob,
+								   auth_data);
+	if (!NT_STATUS_IS_OK(status)) {
+		PyErr_SetNTSTATUS(status);
+		talloc_free(ctx);
+		return NULL;
+	}
+
+	/* Convert the output into Python 'bytes' objects. */
+	py_ciphertext = PyBytes_FromStringAndSize((const char *)ciphertext_blob.data,
+						  ciphertext_blob.length);
+	talloc_free(ctx);
+	if (py_ciphertext == NULL) {
+		return NULL;
+	}
+	py_auth_data = PyBytes_FromStringAndSize((const char *)auth_data,
+						 sizeof(auth_data));
+	if (py_auth_data == NULL) {
+		return NULL;
+	}
+
+	/* Steal ciphertext and auth_data into a new tuple. */
+	py_result = Py_BuildValue("(NN)", py_ciphertext, py_auth_data);
+
+	return py_result;
+}
+
+
+
 static const char py_crypto_arcfour_crypt_blob_doc[] = "arcfour_crypt_blob(data, key)\n"
 					 "Encrypt the data with RC4 algorithm using the key";
 
@@ -201,12 +405,29 @@ static const char py_crypto_des_crypt_blob_16_doc[] = "des_crypt_blob_16(data, k
 static const char py_crypto_md4_hash_blob_doc[] = "md4_hash_blob(data) -> bytes\n"
 						  "Hash the data with MD4 algorithm";
 
+static const char py_crypto_sha512_pbkdf2_doc[] = "sha512_pbkdf2(key, salt, iterations) -> bytes\n"
+						  "Derive a key from an existing one with SHA512 "
+						  "algorithm";
+
+static const char py_crypto_aead_aes_256_cbc_hmac_sha512_blob_doc[] =
+	"aead_aes_256_cbc_hmac_sha512_blob(plaintext, cek, key_salt, "
+	"mac_salt, iv) -> ciphertext, auth_data\n"
+	"Encrypt the plaintext with AES256 as specified in "
+	"[MS-SAMR] 3.2.2.4 AES Cipher Usage";
+
 static PyMethodDef py_crypto_methods[] = {
 	{ "arcfour_crypt_blob", (PyCFunction)py_crypto_arcfour_crypt_blob, METH_VARARGS, py_crypto_arcfour_crypt_blob_doc },
 	{ "set_relax_mode", (PyCFunction)py_crypto_set_relax_mode, METH_NOARGS, "Set fips to relax mode" },
 	{ "set_strict_mode", (PyCFunction)py_crypto_set_strict_mode, METH_NOARGS, "Set fips to strict mode" },
 	{ "des_crypt_blob_16", (PyCFunction)py_crypto_des_crypt_blob_16, METH_VARARGS, py_crypto_des_crypt_blob_16_doc },
 	{ "md4_hash_blob", (PyCFunction)py_crypto_md4_hash_blob, METH_VARARGS, py_crypto_md4_hash_blob_doc },
+	{ "sha512_pbkdf2", (PyCFunction)py_crypto_sha512_pbkdf2, METH_VARARGS, py_crypto_sha512_pbkdf2_doc },
+	{
+		"aead_aes_256_cbc_hmac_sha512_blob",
+		(PyCFunction)py_crypto_aead_aes_256_cbc_hmac_sha512_blob,
+		METH_VARARGS,
+		py_crypto_aead_aes_256_cbc_hmac_sha512_blob_doc
+	},
 	{0},
 };