python - 如何使用 pyasn1 解析 subjectAltName 扩展数据？

Question

我有一些 pyOpenSSL 给我的数据，'0\r\x82\x0bexample.com'. 这应该是 subjectAltName X509 扩展的值。我尝试使用 pyasn1 （并基于 pyasn1 示例之一）对此扩展的 ASN1 规范的必要部分进行编码：

from pyasn1.type import univ, constraint, char, namedtype

from pyasn1.codec.der.decoder import decode

MAX = 64

class DirectoryString(univ.Choice):
    componentType = namedtype.NamedTypes(
        namedtype.NamedType(
            'teletexString', char.TeletexString().subtype(
                subtypeSpec=constraint.ValueSizeConstraint(1, MAX))),
        namedtype.NamedType(
            'printableString', char.PrintableString().subtype(
                subtypeSpec=constraint.ValueSizeConstraint(1, MAX))),
        namedtype.NamedType(
            'universalString', char.UniversalString().subtype(
                subtypeSpec=constraint.ValueSizeConstraint(1, MAX))),
        namedtype.NamedType(
            'utf8String', char.UTF8String().subtype(
                subtypeSpec=constraint.ValueSizeConstraint(1, MAX))),
        namedtype.NamedType(
            'bmpString', char.BMPString().subtype(
                subtypeSpec=constraint.ValueSizeConstraint(1, MAX))),
        namedtype.NamedType(
            'ia5String', char.IA5String().subtype(
                subtypeSpec=constraint.ValueSizeConstraint(1, MAX))),
        )


class AttributeValue(DirectoryString):
    pass


class AttributeType(univ.ObjectIdentifier):
    pass


class AttributeTypeAndValue(univ.Sequence):
    componentType = namedtype.NamedTypes(
        namedtype.NamedType('type', AttributeType()),
        namedtype.NamedType('value', AttributeValue()),
        )


class RelativeDistinguishedName(univ.SetOf):
    componentType = AttributeTypeAndValue()

class RDNSequence(univ.SequenceOf):
    componentType = RelativeDistinguishedName()


class Name(univ.Choice):
    componentType = namedtype.NamedTypes(
        namedtype.NamedType('', RDNSequence()),
        )


class Extension(univ.Sequence):
    componentType = namedtype.NamedTypes(
        namedtype.NamedType('extnID', univ.ObjectIdentifier()),
        namedtype.DefaultedNamedType('critical', univ.Boolean('False')),
        namedtype.NamedType('extnValue', univ.OctetString()),
        )


class Extensions(univ.SequenceOf):
    componentType = Extension()
    sizeSpec = univ.SequenceOf.sizeSpec + constraint.ValueSizeConstraint(1, MAX)


class GeneralName(univ.Choice):
    componentType = namedtype.NamedTypes(
        # namedtype.NamedType('otherName', AnotherName()),
        namedtype.NamedType('rfc822Name', char.IA5String()),
        namedtype.NamedType('dNSName', char.IA5String()),
        # namedtype.NamedType('x400Address', ORAddress()),
        namedtype.NamedType('directoryName', Name()),
        # namedtype.NamedType('ediPartyName', EDIPartyName()),
        namedtype.NamedType('uniformResourceIdentifier', char.IA5String()),
        namedtype.NamedType('iPAddress', univ.OctetString()),
        namedtype.NamedType('registeredID', univ.ObjectIdentifier()),
        )


class GeneralNames(univ.SequenceOf):
    componentType = GeneralName()
    sizeSpec = univ.SequenceOf.sizeSpec + constraint.ValueSizeConstraint(1, MAX)


class SubjectAltName(GeneralNames):
    pass

print decode('0\r\x82\x0bexample.com', asn1Spec=GeneralNames())

显然我在接近尾声时有点无聊，并没有完全指定GeneralName类型。但是，测试字符串应该包含 a dNSName，而不是跳过的值之一，所以我希望没关系。

当程序运行时，它失败并出现我无法解释的错误：

Traceback (most recent call last):
  File "x509.py", line 94, in <module>
    print decode('0\r\x82\x0bexample.com', asn1Spec=GeneralNames())
  File "/usr/lib/pymodules/python2.6/pyasn1/v1/codec/ber/decoder.py", line 493, in __call__
    length, stGetValueDecoder, decodeFun
  File "/usr/lib/pymodules/python2.6/pyasn1/v1/codec/ber/decoder.py", line 202, in valueDecoder
    substrate, asn1Spec
  File "/usr/lib/pymodules/python2.6/pyasn1/v1/codec/ber/decoder.py", line 453, in __call__
    __chosenSpec.getTypeMap().has_key(tagSet):
  File "/usr/lib/pymodules/python2.6/pyasn1/v1/type/univ.py", line 608, in getTypeMap
    return Set.getComponentTypeMap(self)
  File "/usr/lib/pymodules/python2.6/pyasn1/v1/type/univ.py", line 535, in getComponentTypeMap
    def getComponentTypeMap(self): return self._componentType.getTypeMap(1)
  File "/usr/lib/pymodules/python2.6/pyasn1/v1/type/namedtype.py", line 126, in getTypeMap
    'Duplicate type %s in map %s'%(k,self.__typeMap)
pyasn1.error.PyAsn1Error: Duplicate type TagSet(Tag(tagClass=0, tagFormat=0, tagId=22)) in map {TagSet(Tag(tagClass=0, tagFormat=0, tagId=22)): IA5String()}

任何关于我哪里出错以及如何使用 pyasn1 成功解析此扩展类型的提示将不胜感激。

score 15 · Accepted Answer

我在 pyasn1-users 列表上发布了这个问题，Ilya Etingof（pyasn1 的作者）指出了我的错误。简而言之，每个NamedTypein都GeneralName.componentType需要被赋予标签信息。这是通过subtype方法完成的。例如，而不是：

namedtype.NamedType('rfc822Name', char.IA5String()),

定义应该是：

namedtype.NamedType('rfc822Name', char.IA5String().subtype(
        implicitTag=tag.Tag(tag.tagClassContext,
                            tag.tagFormatSimple, 1))),

其中1来自GeneralName的 ASN.1 定义：

GeneralName ::= CHOICE {
   otherName                       [0]     OtherName,
   rfc822Name                      [1]     IA5String,
   dNSName                         [2]     IA5String,
   x400Address                     [3]     ORAddress,
   directoryName                   [4]     Name,
   ediPartyName                    [5]     EDIPartyName,
   uniformResourceIdentifier       [6]     IA5String,
   iPAddress                       [7]     OCTET STRING,
   registeredID                    [8]     OBJECT IDENTIFIER
}

为的每个字段定义标签后componentType，解析成功：

(GeneralNames().setComponentByPosition(
    0, GeneralName().setComponentByPosition(1, IA5String('example.com'))), '')

score 2 · Accepted Answer

这个答案迟到了，但您也可以使用pyasn1-modules 中提供的 RF2459 模块（也由 Ilya Etingof 编写），而不是手动编写 ASN.1 Schema

这段代码至少应该可以工作，并且希望足以让您开始使用更复杂的 ANS.1 结构。确保你已经运行pip install pyasn1，pip install pyasn1-modules否则pip install pyopenssl你会得到导入错误。

# Import pyasn and the proper decode function
import pyasn1
from pyasn1.codec.der.decoder import decode as asn1_decoder

# Import SubjectAltName from rfc2459 module
from pyasn1_modules.rfc2459 import SubjectAltName

# Import native Python type encoder
from pyasn1.codec.native.encoder import encode as nat_encoder

# Import OpenSSL tools for working with certs.
from OpenSSL import crypto
# Read raw certificate file
with open('PATH/TO/CERTIFICATE.crt', 'r') as cert_f:
    raw_cert = cert_f.read()

cert = crypto.load_certificate(crypto.FILETYPE_PEM, raw_cert)

# Note this example assumes SubjectAltName is the only Extension for this cert. 
raw_alt_names = cert.get_extension(0).get_data()

decoded_alt_names, _ = asn1_decoder(raw_alt_names, asn1Spec=SubjectAltName())

# Unless a raw string of ASN.1 is what you need encode back to native Python types
py_alt_names = nat_encoder(decoded_alt_names)

# And Finally a plain Python list of UTF-8 encoded strings representing the SubjectAltNames
subject_alt_names = [ x['dNSName'].decode('utf-8') for x in py_alt_names]

这将是这样的输出

['cdn1.example.com', 'cdn2.example.com']

如果您正在处理的证书有多个扩展，您将需要使用来自 X509 对象的get_extension_count和来自 pyopenssl 中提供的 X509Extension 对象的 get_short_name。

python - 如何使用 pyasn1 解析 subjectAltName 扩展数据？

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