1 files changed, 163 insertions, 0 deletions
diff --git a/tools/mcuboot/imgtool/keys/rsa.py b/tools/mcuboot/imgtool/keys/rsa.py
new file mode 100644
index 00000000..f8273bf5
--- /dev/null
+++ b/tools/mcuboot/imgtool/keys/rsa.py
@@ -0,0 +1,163 @@
+"""
+RSA Key management
+"""
+
+from cryptography.hazmat.backends import default_backend
+from cryptography.hazmat.primitives import serialization
+from cryptography.hazmat.primitives.asymmetric import rsa
+from cryptography.hazmat.primitives.asymmetric.padding import PSS, MGF1
+from cryptography.hazmat.primitives.hashes import SHA256
+
+from .general import KeyClass
+
+
+# Sizes that bootutil will recognize
+RSA_KEY_SIZES = [2048, 3072]
+
+
+class RSAUsageError(Exception):
+    pass
+
+
+class RSAPublic(KeyClass):
+    """The public key can only do a few operations"""
+    def __init__(self, key):
+        self.key = key
+
+    def key_size(self):
+        return self.key.key_size
+
+    def shortname(self):
+        return "rsa"
+
+    def _unsupported(self, name):
+        raise RSAUsageError("Operation {} requires private key".format(name))
+
+    def _get_public(self):
+        return self.key
+
+    def get_public_bytes(self):
+        # The key embedded into MCUboot is in PKCS1 format.
+        return self._get_public().public_bytes(
+            encoding=serialization.Encoding.DER,
+            format=serialization.PublicFormat.PKCS1)
+
+    def get_private_bytes(self, minimal):
+        self._unsupported('get_private_bytes')
+
+    def export_private(self, path, passwd=None):
+        self._unsupported('export_private')
+
+    def export_public(self, path):
+        """Write the public key to the given file."""
+        pem = self._get_public().public_bytes(
+            encoding=serialization.Encoding.PEM,
+            format=serialization.PublicFormat.SubjectPublicKeyInfo)
+        with open(path, 'wb') as f:
+            f.write(pem)
+
+    def sig_type(self):
+        return "PKCS1_PSS_RSA{}_SHA256".format(self.key_size())
+
+    def sig_tlv(self):
+        return"RSA{}".format(self.key_size())
+
+    def sig_len(self):
+        return self.key_size() / 8
+
+    def verify(self, signature, payload):
+        k = self.key
+        if isinstance(self.key, rsa.RSAPrivateKey):
+            k = self.key.public_key()
+        return k.verify(signature=signature, data=payload,
+                        padding=PSS(mgf=MGF1(SHA256()), salt_length=32),
+                        algorithm=SHA256())
+
+
+class RSA(RSAPublic):
+    """
+    Wrapper around an RSA key, with imgtool support.
+    """
+
+    def __init__(self, key):
+        """The key should be a private key from cryptography"""
+        self.key = key
+
+    @staticmethod
+    def generate(key_size=2048):
+        if key_size not in RSA_KEY_SIZES:
+            raise RSAUsageError("Key size {} is not supported by MCUboot"
+                                .format(key_size))
+        pk = rsa.generate_private_key(
+            public_exponent=65537,
+            key_size=key_size,
+            backend=default_backend())
+        return RSA(pk)
+
+    def _get_public(self):
+        return self.key.public_key()
+
+    def _build_minimal_rsa_privkey(self, der):
+        '''
+        Builds a new DER that only includes N/E/D/P/Q RSA parameters;
+        standard DER private bytes provided by OpenSSL also includes
+        CRT params (DP/DQ/QP) which can be removed.
+        '''
+        OFFSET_N = 7  # N is always located at this offset
+        b = bytearray(der)
+        off = OFFSET_N
+        if b[off + 1] != 0x82:
+            raise RSAUsageError("Error parsing N while minimizing")
+        len_N = (b[off + 2] << 8) + b[off + 3] + 4
+        off += len_N
+        if b[off + 1] != 0x03:
+            raise RSAUsageError("Error parsing E while minimizing")
+        len_E = b[off + 2] + 4
+        off += len_E
+        if b[off + 1] != 0x82:
+            raise RSAUsageError("Error parsing D while minimizing")
+        len_D = (b[off + 2] << 8) + b[off + 3] + 4
+        off += len_D
+        if b[off + 1] != 0x81:
+            raise RSAUsageError("Error parsing P while minimizing")
+        len_P = b[off + 2] + 3
+        off += len_P
+        if b[off + 1] != 0x81:
+            raise RSAUsageError("Error parsing Q while minimizing")
+        len_Q = b[off + 2] + 3
+        off += len_Q
+        # adjust DER size for removed elements
+        b[2] = (off - 4) >> 8
+        b[3] = (off - 4) & 0xff
+        return b[:off]
+
+    def get_private_bytes(self, minimal):
+        priv = self.key.private_bytes(
+            encoding=serialization.Encoding.DER,
+            format=serialization.PrivateFormat.TraditionalOpenSSL,
+            encryption_algorithm=serialization.NoEncryption())
+        if minimal:
+            priv = self._build_minimal_rsa_privkey(priv)
+        return priv
+
+    def export_private(self, path, passwd=None):
+        """Write the private key to the given file, protecting it with the
+        optional password."""
+        if passwd is None:
+            enc = serialization.NoEncryption()
+        else:
+            enc = serialization.BestAvailableEncryption(passwd)
+        pem = self.key.private_bytes(
+            encoding=serialization.Encoding.PEM,
+            format=serialization.PrivateFormat.PKCS8,
+            encryption_algorithm=enc)
+        with open(path, 'wb') as f:
+            f.write(pem)
+
+    def sign(self, payload):
+        # The verification code only allows the salt length to be the
+        # same as the hash length, 32.
+        return self.key.sign(
+            data=payload,
+            padding=PSS(mgf=MGF1(SHA256()), salt_length=32),
+            algorithm=SHA256())