scripts: Initial version of Python imgtool
This is the start of a python implementation of imgtool. This
implements all of the functionality that was missing in the zep2newt.py
tool, namely creation of keypairs, and converting the public version of
these keys into C code.
diff --git a/scripts/imgtool/keys.py b/scripts/imgtool/keys.py
new file mode 100644
index 0000000..d529b59
--- /dev/null
+++ b/scripts/imgtool/keys.py
@@ -0,0 +1,126 @@
+"""
+Cryptographic key management for imgtool.
+"""
+
+from Crypto.Hash import SHA256
+from Crypto.PublicKey import RSA
+from Crypto.Signature import PKCS1_v1_5
+from ecdsa import SigningKey, NIST256p, util
+from pyasn1.type import namedtype, univ
+from pyasn1.codec.der.encoder import encode
+
+AUTOGEN_MESSAGE = "/* Autogenerated by imgtool.py, do not edit. */"
+
+class RSAPublicKey(univ.Sequence):
+ componentType = namedtype.NamedTypes(
+ namedtype.NamedType('modulus', univ.Integer()),
+ namedtype.NamedType('publicExponent', univ.Integer()))
+
+class RSA2048():
+ def __init__(self, key):
+ """Construct an RSA2048 key with the given key data"""
+ self.key = key
+
+ @staticmethod
+ def generate():
+ return RSA2048(RSA.generate(2048))
+
+ def export_private(self, path):
+ with open(path, 'wb') as f:
+ f.write(self.key.exportKey('PEM'))
+
+ def emit_c(self):
+ node = RSAPublicKey()
+ node['modulus'] = self.key.n
+ node['publicExponent'] = self.key.e
+ print(AUTOGEN_MESSAGE)
+ print("const unsigned char rsa_pub_key[] = {", end='')
+ encoded = bytearray(encode(node))
+ for count, b in enumerate(encoded):
+ if count % 8 == 0:
+ print("\n\t", end='')
+ else:
+ print(" ", end='')
+ print("0x{:02x},".format(b), end='')
+ print("\n};")
+ print("const unsigned int rsa_pub_key_len = {};".format(len(encoded)))
+
+ def sig_type(self):
+ """Return the type of this signature (as a string)"""
+ return "PKCS15_RSA2048_SHA256"
+
+ def sig_len(self):
+ return 256
+
+ def sig_tlv(self):
+ return "RSA2048"
+
+ def sign(self, payload):
+ sha = SHA256.new(payload)
+ signer = PKCS1_v1_5.new(self.key)
+ signature = signer.sign(sha)
+ assert len(signature) == self.sig_len()
+ return signature
+
+class ECDSA256P1():
+ def __init__(self, key):
+ """Construct an ECDSA P-256 private key"""
+ self.key = key
+
+ @staticmethod
+ def generate():
+ return ECDSA256P1(SigningKey.generate(curve=NIST256p))
+
+ def export_private(self, path):
+ with open(path, 'wb') as f:
+ f.write(key.to_pem())
+
+ def emit_c(self):
+ vk = self.key.get_verifying_key()
+ print(AUTOGEN_MESSAGE)
+ print("const unsigned char ecdsa_pub_key[] = {", end='')
+ encoded = bytes(vk.to_der())
+ for count, b in enumerate(encoded):
+ if count % 8 == 0:
+ print("\n\t", end='')
+ else:
+ print(" ", end='')
+ print("0x{:02x},".format(b), end='')
+ print("\n};")
+ print("const unsigned int ecdsa_pub_key_len = {};".format(len(encoded)))
+
+ def sign(self, payload):
+ # To make this fixed length, possibly pad with zeros.
+ sig = self.key.sign(payload, hashfunc=hashlib.sha256, sigencode=util.sigencode_der)
+ sig += b'\000' * (self.sig_len() - len(sig))
+ return sig
+
+ def sig_len(self):
+ # The DER encoding depends on the high bit, and can be
+ # anywhere from 70 to 72 bytes. Because we have to fill in
+ # the length field before computing the signature, however,
+ # we'll give the largest, and the sig checking code will allow
+ # for it to be up to two bytes larger than the actual
+ # signature.
+ return 72
+
+ def sig_type(self):
+ """Return the type of this signature (as a string)"""
+ return "ECDSA256_SHA256"
+
+ def sig_tlv(self):
+ return "ECDSA256"
+
+def load(path):
+ with open(path, 'rb') as f:
+ pem = f.read()
+ try:
+ key = RSA.importKey(pem)
+ if key.n.bit_length() != 2048:
+ raise Exception("Unsupported RSA bit length, only 2048 supported")
+ return RSA2048(key)
+ except ValueError:
+ key = SigningKey.from_pem(pem)
+ if key.curve.name != 'NIST256p':
+ raise Exception("Unsupported ECDSA curve")
+ return ECDSA256P1(key)