imgtool: Add rust pubkey generation

Add a `--rust` flag to the getpub subcommand to output the public key in
Rust format rather than C.

Signed-off-by: David Brown <david.brown@linaro.org>

scripts/imgtool.py

@@ -26,7 +26,13 @@ def do_keygen(args):
 
 def do_getpub(args):
     key = keys.load(args.key)
-    key.emit_c()
+    if args.lang == 'c':
+        key.emit_c()
+    elif args.lang == 'rust':
+        key.emit_rust()
+    else:
+        msg = "Unsupported language, valid are: c, or rust"
+        raise argparse.ArgumentTypeError(msg)
 
 def do_sign(args):
     if args.rsa_pkcs1_15:
@@ -73,6 +79,7 @@ def args():
 
     getpub = subs.add_parser('getpub', help='Get public key from keypair')
     getpub.add_argument('-k', '--key', metavar='filename', required=True)
+    getpub.add_argument('-l', '--lang', metavar='lang', default='c')
 
     sign = subs.add_parser('sign', help='Sign an image with a private key')
     sign.add_argument('-k', '--key', metavar='filename')

scripts/imgtool/keys.py

@@ -34,13 +34,16 @@ class RSA2048():
         with open(path, 'wb') as f:
             f.write(self.key.exportKey('PEM'))
 
-    def emit_c(self):
+    def get_public_bytes(self):
         node = RSAPublicKey()
         node['modulus'] = self.key.n
         node['publicExponent'] = self.key.e
+        return bytearray(encode(node))
+
+    def emit_c(self):
         print(AUTOGEN_MESSAGE)
         print("const unsigned char rsa_pub_key[] = {", end='')
-        encoded = bytearray(encode(node))
+        encoded = self.get_public_bytes()
         for count, b in enumerate(encoded):
             if count % 8 == 0:
                 print("\n\t", end='')
@@ -50,6 +53,18 @@ class RSA2048():
         print("\n};")
         print("const unsigned int rsa_pub_key_len = {};".format(len(encoded)))
 
+    def emit_rust(self):
+        print(AUTOGEN_MESSAGE)
+        print("static RSA_PUB_KEY: &'static [u8] = &[", end='')
+        encoded = self.get_public_bytes()
+        for count, b in enumerate(encoded):
+            if count % 8 == 0:
+                print("\n    ", end='')
+            else:
+                print(" ", end='')
+            print("0x{:02x},".format(b), end='')
+        print("\n];")
+
     def sig_type(self):
         """Return the type of this signature (as a string)"""
         if sign_rsa_pss: