Split ASN.1 utilities out into their own file.

dkim/__init__.py

@@ -1,21 +1,3 @@
-# This software is provided 'as-is', without any express or implied
-# warranty.  In no event will the author be held liable for any damages
-# arising from the use of this software.
-# 
-# Permission is granted to anyone to use this software for any purpose,
-# including commercial applications, and to alter it and redistribute it
-# freely, subject to the following restrictions:
-# 
-# 1. The origin of this software must not be misrepresented; you must not
-#    claim that you wrote the original software. If you use this software
-#    in a product, an acknowledgment in the product documentation would be
-#    appreciated but is not required.
-# 2. Altered source versions must be plainly marked as such, and must not be
-#    misrepresented as being the original software.
-# 3. This notice may not be removed or altered from any source distribution.
-# 
-# Copyright (c) 2008 Greg Hewgill http://hewgill.com
-
 import base64
 import hashlib
 import re
@@ -23,6 +5,17 @@ import time
 
 import dns.resolver
 
+from dkim.asn1 import (
+    asn1_build,
+    asn1_parse,
+    BIT_STRING,
+    INTEGER,
+    SEQUENCE,
+    OBJECT_IDENTIFIER,
+    OCTET_STRING,
+    NULL,
+    )
+
 __all__ = [
     "Simple",
     "Relaxed",
@@ -208,13 +201,6 @@ def validate_signature_fields(sig, debuglog=None):
     return True
 
 
-INTEGER = 0x02
-BIT_STRING = 0x03
-OCTET_STRING = 0x04
-NULL = 0x05
-OBJECT_IDENTIFIER = 0x06
-SEQUENCE = 0x30
-
 ASN1_Object = [
     (SEQUENCE, [
         (SEQUENCE, [
@@ -246,80 +232,6 @@ ASN1_RSAPrivateKey = [
     ])
 ]
 
-def asn1_parse(template, data):
-    """Parse a data structure according to ASN.1 template.
-
-    @param template: A list of tuples comprising the ASN.1 template.
-    @param data: A list of bytes to parse.
-
-    """
-
-    r = []
-    i = 0
-    for t in template:
-        tag = ord(data[i])
-        i += 1
-        if tag == t[0]:
-            length = ord(data[i])
-            i += 1
-            if length & 0x80:
-                n = length & 0x7f
-                length = 0
-                for j in range(n):
-                    length = (length << 8) | ord(data[i])
-                    i += 1
-            if tag == INTEGER:
-                n = 0
-                for j in range(length):
-                    n = (n << 8) | ord(data[i])
-                    i += 1
-                r.append(n)
-            elif tag == BIT_STRING:
-                r.append(data[i:i+length])
-                i += length
-            elif tag == NULL:
-                assert length == 0
-                r.append(None)
-            elif tag == OBJECT_IDENTIFIER:
-                r.append(data[i:i+length])
-                i += length
-            elif tag == SEQUENCE:
-                r.append(asn1_parse(t[1], data[i:i+length]))
-                i += length
-            else:
-                raise KeyFormatError("Unexpected tag in template: %02x" % tag)
-        else:
-            raise KeyFormatError("Unexpected tag (got %02x, expecting %02x)" % (tag, t[0]))
-    return r
-
-def asn1_length(n):
-    """Return a string representing a field length in ASN.1 format."""
-    assert n >= 0
-    if n < 0x7f:
-        return chr(n)
-    r = ""
-    while n > 0:
-        r = chr(n & 0xff) + r
-        n >>= 8
-    return r
-
-def asn1_build(node):
-    """Build an ASN.1 data structure based on pairs of (type, data)."""
-    if node[0] == OCTET_STRING:
-        return chr(OCTET_STRING) + asn1_length(len(node[1])) + node[1]
-    if node[0] == NULL:
-        assert node[1] is None
-        return chr(NULL) + asn1_length(0)
-    elif node[0] == OBJECT_IDENTIFIER:
-        return chr(OBJECT_IDENTIFIER) + asn1_length(len(node[1])) + node[1]
-    elif node[0] == SEQUENCE:
-        r = ""
-        for x in node[1]:
-            r += asn1_build(x)
-        return chr(SEQUENCE) + asn1_length(len(r)) + r
-    else:
-        raise InternalError("Unexpected tag in template: %02x" % node[0])
-
 # These values come from RFC 3447, section 9.2 Notes, page 43.
 HASHID_SHA1 = "\x2b\x0e\x03\x02\x1a"
 HASHID_SHA256 = "\x60\x86\x48\x01\x65\x03\x04\x02\x01"

dkim/asn1.py

@@ -0,0 +1,119 @@
+# This software is provided 'as-is', without any express or implied
+# warranty.  In no event will the author be held liable for any damages
+# arising from the use of this software.
+#
+# Permission is granted to anyone to use this software for any purpose,
+# including commercial applications, and to alter it and redistribute it
+# freely, subject to the following restrictions:
+#
+# 1. The origin of this software must not be misrepresented; you must not
+#    claim that you wrote the original software. If you use this software
+#    in a product, an acknowledgment in the product documentation would be
+#    appreciated but is not required.
+# 2. Altered source versions must be plainly marked as such, and must not be
+#    misrepresented as being the original software.
+# 3. This notice may not be removed or altered from any source distribution.
+#
+# Copyright (c) 2008 Greg Hewgill http://hewgill.com
+
+__all__ = [
+    'asn1_build',
+    'asn1_parse',
+    'ASN1FormatError',
+    'BIT_STRING',
+    'INTEGER',
+    'SEQUENCE',
+    'OBJECT_IDENTIFIER',
+    'OCTET_STRING',
+    'NULL',
+    ]
+
+INTEGER = 0x02
+BIT_STRING = 0x03
+OCTET_STRING = 0x04
+NULL = 0x05
+OBJECT_IDENTIFIER = 0x06
+SEQUENCE = 0x30
+
+
+class ASN1FormatError(Exception):
+    pass
+
+
+def asn1_parse(template, data):
+    """Parse a data structure according to ASN.1 template.
+
+    @param template: A list of tuples comprising the ASN.1 template.
+    @param data: A list of bytes to parse.
+
+    """
+
+    r = []
+    i = 0
+    for t in template:
+        tag = ord(data[i])
+        i += 1
+        if tag == t[0]:
+            length = ord(data[i])
+            i += 1
+            if length & 0x80:
+                n = length & 0x7f
+                length = 0
+                for j in range(n):
+                    length = (length << 8) | ord(data[i])
+                    i += 1
+            if tag == INTEGER:
+                n = 0
+                for j in range(length):
+                    n = (n << 8) | ord(data[i])
+                    i += 1
+                r.append(n)
+            elif tag == BIT_STRING:
+                r.append(data[i:i+length])
+                i += length
+            elif tag == NULL:
+                assert length == 0
+                r.append(None)
+            elif tag == OBJECT_IDENTIFIER:
+                r.append(data[i:i+length])
+                i += length
+            elif tag == SEQUENCE:
+                r.append(asn1_parse(t[1], data[i:i+length]))
+                i += length
+            else:
+                raise ASN1FormatError(
+                    "Unexpected tag in template: %02x" % tag)
+        else:
+            raise ASN1FormatError(
+                "Unexpected tag (got %02x, expecting %02x)" % (tag, t[0]))
+    return r
+
+
+def asn1_length(n):
+    """Return a string representing a field length in ASN.1 format."""
+    assert n >= 0
+    if n < 0x7f:
+        return chr(n)
+    r = ""
+    while n > 0:
+        r = chr(n & 0xff) + r
+        n >>= 8
+    return r
+
+
+def asn1_build(node):
+    """Build an ASN.1 data structure based on pairs of (type, data)."""
+    if node[0] == OCTET_STRING:
+        return chr(OCTET_STRING) + asn1_length(len(node[1])) + node[1]
+    if node[0] == NULL:
+        assert node[1] is None
+        return chr(NULL) + asn1_length(0)
+    elif node[0] == OBJECT_IDENTIFIER:
+        return chr(OBJECT_IDENTIFIER) + asn1_length(len(node[1])) + node[1]
+    elif node[0] == SEQUENCE:
+        r = ""
+        for x in node[1]:
+            r += asn1_build(x)
+        return chr(SEQUENCE) + asn1_length(len(r)) + r
+    else:
+        raise ASN1FormatError("Unexpected tag in template: %02x" % node[0])