test_suite_pk: add python script to generate predefined keys

This commit adds "generate_test_keys.py" script to generate
predefined keys used in test_suite_pk. Keys are generated with
"programs/pkey/gen_key" tool and converted to C array using
the python script.

tests/src/test_keys.h is automatically generated using the
above mentioned script.

test_suite_pk is updated in order to use the new format.

Signed-off-by: Valerio Setti <valerio.setti@nordicsemi.no>
diff --git a/tests/scripts/generate_test_keys.py b/tests/scripts/generate_test_keys.py
new file mode 100755
index 0000000..c2d23c9
--- /dev/null
+++ b/tests/scripts/generate_test_keys.py
@@ -0,0 +1,103 @@
+#!/usr/bin/env python3
+
+# Copyright The Mbed TLS Contributors
+# SPDX-License-Identifier: Apache-2.0 OR GPL-2.0-or-later
+
+"""Module generating EC and RSA keys to be used in test_suite_pk instead of
+generating the required key at run time. This helps speeding up testing."""
+
+import os
+import sys
+import subprocess
+
+KEY_GEN = "./programs/pkey/gen_key"
+TMP_DER_FILE = "tmp_key.der"
+OUTPUT_HEADER_FILE = "./tests/src/test_keys.h"
+BYTES_PER_LINE = 12
+
+KEYS = {
+    # RSA keys
+    'test_rsa_1024': ['rsa', '1024'],
+    'test_rsa_1026': ['rsa', '1026'],
+    'test_rsa_1028': ['rsa', '1028'],
+    'test_rsa_1030': ['rsa', '1030'],
+    'test_rsa_2048': ['rsa', '2048'],
+    'test_rsa_4096': ['rsa', '4096'],
+    # EC keys
+    'test_ec_secp192r1': ['ec', 'secp192r1'],
+    'test_ec_secp224r1': ['ec', 'secp224r1'],
+    'test_ec_secp256r1': ['ec', 'secp256r1'],
+    'test_ec_secp384r1': ['ec', 'secp384r1'],
+    'test_ec_secp521r1': ['ec', 'secp521r1'],
+    'test_ec_bp256r1': ['ec', 'brainpoolP256r1'],
+    'test_ec_bp384r1': ['ec', 'brainpoolP384r1'],
+    'test_ec_bp512r1': ['ec', 'brainpoolP512r1'],
+    'test_ec_curve25519': ['ec', 'x25519'],
+    'test_ec_secp192k1': ['ec', 'secp192k1'],
+    'test_ec_secp256k1': ['ec', 'secp256k1'],
+    'test_ec_curve448': ['ec', 'x448'],
+}
+
+def generate_der_file(curve_type: str, curve_or_bits: str):
+    if not os.path.exists(KEY_GEN):
+        raise Exception("Key generation program does not exist.")
+    if curve_type == 'ec':
+        cob_param = 'ec_curve=' + curve_or_bits
+    else:
+        cob_param = 'rsa_keysize=' + curve_or_bits
+
+    subprocess.run([KEY_GEN, 'type=' + curve_type, cob_param,
+                    'format=der', 'filename=' + TMP_DER_FILE], check=True)
+
+def convert_der_to_c(array_name: str) -> str:
+    """Convert a DER file content to a C array. The name of such array is
+    provided as input parameter. The file to be converted is the temporary
+    TMP_DER_FILE."""
+    output_text = "const unsigned char {}[] = {{\n".format(array_name)
+
+    with open(TMP_DER_FILE, 'rb') as input_file:
+        data_block = input_file.read(BYTES_PER_LINE)
+        while data_block:
+            new_line = '    ' + ', '.join(['{:#04x}'.format(b) for b in data_block])
+            output_text = output_text + new_line + ",\n"
+            data_block = input_file.read(BYTES_PER_LINE)
+
+    output_text = output_text + "};\n"
+
+    return output_text
+
+def write_header(macro_name: str):
+    return ("/* This macro was generated from tests/scripts/generate_test_keys.py */\n" +
+            "/* BEGIN FILE string macro {} */\n".format(macro_name))
+
+def write_footer():
+    return "/* END FILE */\n"
+
+def main():
+    # Remove intermediate and output files if already existing.
+    if os.path.exists(OUTPUT_HEADER_FILE):
+        os.remove(OUTPUT_HEADER_FILE)
+    if os.path.exists(TMP_DER_FILE):
+        os.remove(TMP_DER_FILE)
+
+    output_file = open(OUTPUT_HEADER_FILE, 'at')
+
+    add_newline = False
+    for key in KEYS:
+        # Use gen_key tool to generate the desired key (in DER format) and save
+        # it into a temporary file.
+        generate_der_file(KEYS[key][0], KEYS[key][1])
+        # Convert the key from binary format to a C array and append the result
+        # to the output header file.
+        if add_newline:
+            output_file.write("\n")
+        output_file.write(write_header(key))
+        c_data = convert_der_to_c(key)
+        output_file.write(c_data)
+        output_file.write(write_footer())
+        # Remove the temporary key file.
+        os.remove(TMP_DER_FILE)
+        add_newline = True
+
+if __name__ == '__main__':
+    sys.exit(main())