Updater signature validation - format incompatible w/RFC8017 (#6250)

* Add hash OID to signature verification (#6201)

* Add legacy signing option

* Describe and use the legacy option of signing.py

cores/esp8266/Updater.h

@@ -38,6 +38,7 @@ class UpdaterHashClass {
     virtual void end() = 0;
     virtual int len() = 0;
     virtual const void *hash() = 0;
+    virtual const unsigned char *oid() = 0;
 };
 
 // Abstract class to implement a signature verifier

doc/ota_updates/readme.rst

@@ -125,6 +125,18 @@ Compile the sketch normally and, once a `.bin` file is available, sign it using
 
     <ESP8266ArduioPath>/tools/signing.py --mode sign --privatekey <path-to-private.key> --bin <path-to-unsigned-bin> --out <path-to-signed-binary>
 
+Old And New Signature Formats
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Up to version 2.5.2 of the core, the format of signatures was a little different. An additional signed binary with the extension legacy_sig is created. This file contains a signature in the old format and can be uploaded OTA to a device that checks for the old signature format.
+
+To create a legacy signature, call the signing script with --legacy:
+
+.. code:: bash
+
+    <ESP8266ArduioPath>/tools/signing.py --mode sign --privatekey <path-to-private.key> --bin <path-to-unsigned-bin> --out <path-to-signed-binary> --legacy <path-to-legacy-file>
+
+
 Safety
 ~~~~~~
 

libraries/ESP8266WiFi/src/BearSSLHelpers.cpp

@@ -848,6 +848,10 @@ const void *HashSHA256::hash() {
   return (const void*) _sha256;
 }
 
+const unsigned char *HashSHA256::oid() {
+    return BR_HASH_OID_SHA256;
+}
+
 // SHA256 verifier
 uint32_t SigningVerifier::length()
 {
@@ -869,7 +873,7 @@ bool SigningVerifier::verify(UpdaterHashClass *hash, const void *signature, uint
     bool ret;
     unsigned char vrf[hash->len()];
     br_rsa_pkcs1_vrfy vrfy = br_rsa_pkcs1_vrfy_get_default();
-    ret = vrfy((const unsigned char *)signature, signatureLen, NULL, sizeof(vrf), _pubKey->getRSA(), vrf);
+    ret = vrfy((const unsigned char *)signature, signatureLen, hash->oid(), sizeof(vrf), _pubKey->getRSA(), vrf);
     if (!ret || memcmp(vrf, hash->hash(), sizeof(vrf)) ) {
       return false;
     } else {
@@ -896,4 +900,4 @@ make_stack_thunk(br_ssl_engine_sendrec_buf);
 
 #endif
 
-};
+};

libraries/ESP8266WiFi/src/BearSSLHelpers.h

@@ -146,6 +146,7 @@ class HashSHA256 : public UpdaterHashClass {
     virtual void end() override;
     virtual int len() override;
     virtual const void *hash() override;
+    virtual const unsigned char *oid() override;
   private:
     br_sha256_context _cc;
     unsigned char _sha256[32];

platform.txt

@@ -109,7 +109,7 @@ recipe.objcopy.eep.pattern=
 
 ## Create hex
 recipe.objcopy.hex.1.pattern="{runtime.tools.python.path}/python" "{runtime.tools.elf2bin}" --eboot "{runtime.tools.eboot}" --app "{build.path}/{build.project_name}.elf" --flash_mode {build.flash_mode} --flash_freq {build.flash_freq} --flash_size {build.flash_size} --path "{runtime.tools.xtensa-lx106-elf-gcc.path}/bin" --out "{build.path}/{build.project_name}.bin"
-recipe.objcopy.hex.2.pattern="{runtime.tools.python.path}/python" "{runtime.tools.signing}" --mode sign --privatekey "{build.source.path}/private.key" --bin "{build.path}/{build.project_name}.bin" --out "{build.path}/{build.project_name}.bin.signed"
+recipe.objcopy.hex.2.pattern="{runtime.tools.python.path}/python" "{runtime.tools.signing}" --mode sign --privatekey "{build.source.path}/private.key" --bin "{build.path}/{build.project_name}.bin" --out "{build.path}/{build.project_name}.bin.signed" --legacy "{build.path}/{build.project_name}.bin.legacy_sig"
 
 ## Save hex
 recipe.output.tmp_file={build.project_name}.bin

tools/signing.py

@@ -12,10 +12,43 @@ def parse_args():
     parser.add_argument('-m', '--mode', help='Mode (header, sign)')
     parser.add_argument('-b', '--bin', help='Unsigned binary')
     parser.add_argument('-o', '--out', help='Output file');
+    parser.add_argument('-l', '--legacy', help='Legacy output file');
     parser.add_argument('-p', '--publickey', help='Public key file');
     parser.add_argument('-s', '--privatekey', help='Private(secret) key file');
     return parser.parse_args()
 
+def sign_and_write(data, priv_key, out_file):
+    """Signs the data (bytes) with the private key (file path)."""
+    """Save the signed firmware to out_file (file path)."""
+
+    signcmd = [ 'openssl', 'dgst', '-sha256', '-sign', priv_key ]
+    proc = subprocess.Popen(signcmd, stdout=subprocess.PIPE, stdin=subprocess.PIPE, stderr=subprocess.PIPE)
+    signout, signerr = proc.communicate(input=data)
+    if proc.returncode:
+        sys.stderr.write("OpenSSL returned an error signing the binary: " + str(proc.returncode) + "\nSTDERR: " + str(signerr))
+    else:
+        with open(out_file, "wb") as out:
+            out.write(data)
+            out.write(signout)
+            out.write(b'\x00\x01\x00\x00')
+            sys.stderr.write("Signed binary: " + out_file + "\n")
+
+def sign_and_write_legacy(data, priv_key, out_file):
+    """Signs the data (bytes) with the private key (file path)."""
+    """Save the signed firmware to out_file (file path)."""
+
+    sha256 = hashlib.sha256(data)
+    signcmd = [ 'openssl', 'rsautl', '-sign', '-inkey', priv_key ]
+    proc = subprocess.Popen(signcmd, stdout=subprocess.PIPE, stdin=subprocess.PIPE, stderr=subprocess.PIPE)
+    signout, signerr = proc.communicate(input=sha256.digest())
+    if proc.returncode:
+        sys.stderr.write("OpenSSL returned an error legacy signing the binary: " + str(proc.returncode) + "\nSTDERR: " + str(signerr))
+    else:
+        with open(out_file, "wb") as out:
+            out.write(data)
+            out.write(signout)
+            out.write(b'\x00\x01\x00\x00')
+            sys.stderr.write("Legacy signed binary: " + out_file + "\n")
 
 def main():
     args = parse_args()
@@ -51,18 +84,12 @@ def main():
         try:
             with open(args.bin, "rb") as b:
                 bin = b.read()
-                sha256 = hashlib.sha256(bin)
-                signcmd = [ 'openssl', 'rsautl', '-sign', '-inkey', args.privatekey ]
-                proc = subprocess.Popen(signcmd, stdout=subprocess.PIPE, stdin=subprocess.PIPE, stderr=subprocess.PIPE)
-                signout, signerr = proc.communicate(input=sha256.digest())
-                if proc.returncode:
-                    sys.stderr.write("OpenSSL returned an error signing the binary: " + str(proc.returncode) + "\nSTDERR: " + str(signerr))
-                else:
-                    with open(args.out, "wb") as out:
-                        out.write(bin)
-                        out.write(signout)
-                        out.write(b'\x00\x01\x00\x00')
-                        sys.stderr.write("Signed binary: " + args.out + "\n")
+
+                sign_and_write(bin, args.privatekey, args.out)
+
+                if args.legacy:
+                    sign_and_write_legacy(bin, args.privatekey, args.legacy)
+
         except Exception as e:
             sys.stderr.write(str(e))
             sys.stderr.write("Not signing the generated binary\n")