/* Part of SWI-Prolog
Author: Matt Lilley
E-mail: thetrime@gmail.com
WWW: http://www.swi-prolog.org
Copyright (c) 2004-2016, SWI-Prolog Foundation
VU University Amsterdam
All rights reserved.
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modification, are permitted provided that the following conditions
are met:
1. Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in
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distribution.
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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*/
:-module(xmlenc,
[ decrypt_xml/4, % +EncryptedXML, -DecryptedXML, :KeyCallback, +Options
load_certificate_from_base64_string/2 % +Base64String, -Certificate
]).
:- autoload(library(base64),[base64/2]).
:- autoload(library(crypto),
[crypto_data_decrypt/6,rsa_private_decrypt/4,hex_bytes/2]).
:- autoload(library(error),[existence_error/2,domain_error/2]).
:- autoload(library(lists),[append/3]).
:- autoload(library(sgml),[load_structure/3]).
:- autoload(library(ssl),[load_certificate/2]).
:- autoload(library(uri),[uri_components/2]).
:- autoload(library(http/http_open),[http_open/3]).
:- meta_predicate
decrypt_xml(+, -, 3, +).
/** <module> XML encryption library
This library is a partial implementation of the XML encryption standard.
It implements the _decryption_ part, which is needed by SAML clients.
@see https://www.w3.org/TR/xmlenc-core1/
@see https://en.wikipedia.org/wiki/Security_Assertion_Markup_Language
*/
% These are the 4 mandatory block cipher algorithms
% (actually aes-192-cbc is not mandatory, but it is easy to support)
ssl_algorithm('http://www.w3.org/2001/04/xmlenc#tripledes-cbc', 'des3', 8).
ssl_algorithm('http://www.w3.org/2001/04/xmlenc#aes128-cbc', 'aes-128-cbc', 16).
ssl_algorithm('http://www.w3.org/2001/04/xmlenc#aes256-cbc', 'aes-256-cbc', 32).
ssl_algorithm('http://www.w3.org/2001/04/xmlenc#aes192-cbc', 'aes-192-cbc', 24).
%! decrypt_xml(+DOMIn, -DOMOut, :KeyCallback, +Options) is det.
%
% @arg KeyCallback may be called as follows:
% - call(KeyCallback, name, KeyName, Key)
% - call(KeyCallback, public_key, public_key(RSA), Key)
% - call(KeyCallback, certificate, Certificate, Key)
decrypt_xml([], [], _, _):- !.
decrypt_xml([element(ns(_, 'http://www.w3.org/2001/04/xmlenc#'):'EncryptedData',
Attributes, EncryptedData)|Siblings],
[Decrypted|NewSiblings], KeyCallback, Options) :-
!,
decrypt_element(Attributes, EncryptedData, Decrypted, KeyCallback, Options),
decrypt_xml(Siblings, NewSiblings, KeyCallback, Options).
decrypt_xml([element(Tag, Attributes, Children)|Siblings],
[element(Tag, Attributes, NewChildren)|NewSiblings], KeyCallback, Options) :-
!,
decrypt_xml(Children, NewChildren, KeyCallback, Options),
decrypt_xml(Siblings, NewSiblings, KeyCallback, Options).
decrypt_xml([Other|Siblings], [Other|NewSiblings], KeyCallback, Options):-
decrypt_xml(Siblings, NewSiblings, KeyCallback, Options).
%! decrypt_element(+Attributes,
%! +EncryptedData,
%! -DecryptedElement,
%! +Options).
%
% Decrypt an EncryptedData element with Attributes and child
% EncryptedData DecryptedElement will either be an element/3 term
% or a string as dictacted by the Type attribute in Attributes.
% If Attributes does not contain a Type attribute then we assume
% it is a string
:-meta_predicate(decrypt_element(+, +, -, 3, +)).
decrypt_element(Attributes, EncryptedData, Decrypted, KeyCallback, Options):-
XENC = ns(_, 'http://www.w3.org/2001/04/xmlenc#'),
( memberchk(element(XENC:'CipherData', _, CipherData), EncryptedData)
-> true
; existence_error(cipher_data, EncryptedData)
),
% The Type attribute is not mandatory. However, 3.1 states that
% "Without this information, the decryptor will be unable to automatically restore the XML document to its original cleartext form."
( memberchk('Type'=Type, Attributes)
-> true
; Type = 'http://www.w3.org/2001/04/xmlenc#Content'
),
% First of all, determine the algorithm used to encrypt the data
determine_encryption_algorithm(EncryptedData, Algorithm, IVSize),
% There are now two tasks remaining, and they seem like they ought to be quite simple, but unfortunately they are not
% First, we must determine the key used to encrypt the message
determine_key(EncryptedData, Key, KeyCallback, Options),
% Then, we must determine what the encrypted data even IS
% If the message includes a CipherValue then this is straightfoward - the encrypted data is the base64-encoded child
% of this element.
( memberchk(element(XENC:'CipherValue', _, CipherValueElement), CipherData)
-> base64_element(CipherValueElement, CipherValueWithIV),
string_codes(CipherValueWithIV, CipherValueWithIVCodes),
length(IVCodes, IVSize),
append(IVCodes, CipherCodes, CipherValueWithIVCodes),
string_codes(IV, IVCodes),
string_codes(CipherText, CipherCodes),
length(CipherValueWithIVCodes, _),
crypto_data_decrypt(CipherText, Algorithm, Key, IV, DecryptedStringWithPadding, [padding(none), encoding(octet)])
; memberchk(element(XENC:'CipherReference', CipherReferenceAttributes, CipherReference), CipherData)->
% However, it is allowed to include CipherReference instead. This is an arbitrary URI and a list of transforms to convert the
% data identified by that URI into the raw octets that represent the encrypted data
% The URI attribute of the CipherReference element is mandatory
memberchk('URI'=CipherURI, CipherReferenceAttributes),
% The transforms attribute is optional, though.
( memberchk(element('Transforms', _, Transforms), CipherReference)
-> true
; Transforms = []
),
uri_components(CipherURI, uri_components(Scheme, _, _, _, _)),
( ( Scheme == 'http' ; Scheme == 'https')
% FIXME: URI may not be an *absolute* URL
-> with_output_to(string(RawCipherValue),
setup_call_cleanup(http_open(CipherURI, HTTPStream, []),
copy_stream_data(HTTPStream, current_output),
close(HTTPStream)))
; domain_error(resolvable_uri, CipherURI)
),
apply_ciphertext_transforms(RawCipherValue, Transforms, CipherValue),
sub_string(CipherValue, 0, IVSize, _, IV),
sub_string(CipherValue, IVSize, _, 0, CipherText),
crypto_data_decrypt(CipherText, Algorithm, Key, IV, DecryptedStringWithPadding, [padding(none), encoding(octet)])
),
% The XML-ENC padding scheme does not comply with RFC-1423. This has been noted a few times by people trying to write
% XML-ENC decryptors backed by OpenSSL, which insists on compliance. The only recourse we have is to disable padding entirely
% and do it in our application
xmlenc_padding(DecryptedStringWithPadding, DecryptedString),
% Now that we have the decrypted data, we can decide whether to turn it into an element or leave it as
% content
( Type == 'http://www.w3.org/2001/04/xmlenc#Element'
-> setup_call_cleanup(open_string(DecryptedString, StringStream),
load_structure(StringStream, [Decrypted], [dialect(xmlns), keep_prefix(true)]),
close(StringStream))
; Decrypted = DecryptedString
).
xmlenc_padding(DecryptedStringWithPadding, DecryptedString):-
string_length(DecryptedStringWithPadding, _),
string_codes(DecryptedStringWithPadding, Codes),
append(_, [LastCode], Codes),
length(Padding, LastCode),
append(DecryptedCodes, Padding, Codes),
!,
string_codes(DecryptedString, DecryptedCodes).
apply_ciphertext_transforms(CipherValue, [], CipherValue):- !.
apply_ciphertext_transforms(_, [_AnythingElse|_], _):-
% FIXME: Not implemented
throw(error(implementation_missing('CipherReference transforms are not implemented', _))).
:- meta_predicate determine_key(+,-,3,+).
determine_key(EncryptedData, Key, KeyCallback, Options):-
DS = ns(_, 'http://www.w3.org/2000/09/xmldsig#'),
( memberchk(element(DS:'KeyInfo', _, KeyInfo), EncryptedData)
-> true
; % Technically the KeyInfo is not mandatory. However, without a key we cannot decrypt
% so raise an error. In the future Options could contain a key if it is agreed upon
% by some other channel
existence_error(key_info, EncryptedData)
),
resolve_key(KeyInfo, Key, KeyCallback, Options).
:- meta_predicate resolve_key(+,-,3,+).
resolve_key(Info, Key, KeyCallback, Options):-
% EncryptedKey
XENC = 'http://www.w3.org/2001/04/xmlenc#',
memberchk(element(ns(_, XENC):'EncryptedKey', _KeyAttributes, EncryptedKey), Info),
!,
% The EncryptedKey is slightly different to EncryptedData. For a start, the algorithms used to decrypt the
% key are orthogonal to those used for EncryptedData. However we can recursively search for the keys then
% decrypt them using the different algorithms as needed
memberchk(element(ns(_, XENC):'EncryptionMethod', MethodAttributes, EncryptionMethod), EncryptedKey),
memberchk('Algorithm'=Algorithm, MethodAttributes),
% Now find the KeyInfo
determine_key(EncryptedKey, PrivateKey, KeyCallback, Options),
memberchk(element(ns(_, XENC):'CipherData', _, CipherData), EncryptedKey),
memberchk(element(ns(_, XENC):'CipherValue', _, CipherValueElement), CipherData),
base64_element(CipherValueElement, CipherValue),
( Algorithm == 'http://www.w3.org/2001/04/xmlenc#rsa-oaep-mgf1p'
-> rsa_private_decrypt(PrivateKey, CipherValue, Key, [encoding(octet), padding(pkcs1_oaep)])
; Algorithm == 'http://www.w3.org/2009/xmlenc11#rsa-oaep',
memberchk(element(ns(_, 'http://www.w3.org/2009/xmlenc11#'):'MGF', MGFAttributes, _), EncryptionMethod),
memberchk('Algorithm'='http://www.w3.org/2009/xmlenc11#mgf1sha1', MGFAttributes) % This is just the same as rsa-oaep-mgf1p!
-> rsa_private_decrypt(PrivateKey, CipherValue, Key, [encoding(octet), padding(pkcs1_oaep)])
; Algorithm == 'http://www.w3.org/2001/04/xmlenc#rsa-1_5'
-> rsa_private_decrypt(PrivateKey, CipherValue, Key, [encoding(octet), padding(pkcs1)])
; domain_error(key_transport, Algorithm)
).
resolve_key(KeyInfo, _Key, _KeyCallback, _Options):-
% AgreementMethod. FIXME: Not implemented
XENC = ns(_, 'http://www.w3.org/2001/04/xmlenc#'),
memberchk(element(XENC:'AgreementMethod', _KeyAttributes, _AgreementMethod), KeyInfo),
!,
throw(not_implemented).
% Additionally, we are allowed to use any elements from XML-DSIG
resolve_key(KeyInfo, Key, KeyCallback, _Options):-
% KeyName. Use the callback with type=name and hint=KeyName
DS = ns(_, 'http://www.w3.org/2000/09/xmldsig#'),
memberchk(element(DS:'KeyName', _KeyAttributes, [KeyName]), KeyInfo),
!,
call(KeyCallback, name, KeyName, Key).
resolve_key(KeyInfo, _Key, _KeyCallback, _Options):-
% RetrievalMethod. FIXME: Not implemented
DS = ns(_, 'http://www.w3.org/2000/09/xmldsig#'),
memberchk(element(DS:'RetrievalMethod', _KeyAttributes, _RetrievalMethod), KeyInfo),
!,
throw(not_implemented).
resolve_key(KeyInfo, Key, KeyCallback, _Options):-
% KeyValue.
DS = ns(_, 'http://www.w3.org/2000/09/xmldsig#'),
memberchk(element(DS:'KeyValue', _KeyAttributes, KeyValue), KeyInfo),
!,
( memberchk(element(DS:'RSAKeyValue', _, RSAKeyValue), KeyInfo)
-> memberchk(element(DS:'Modulus', _, [ModulusBase64]), RSAKeyValue),
memberchk(element(DS:'Exponent', _, [ExponentBase64]), RSAKeyValue),
base64_to_hex(ModulusBase64, Modulus),
base64_to_hex(ExponentBase64, Exponent),
call(KeyCallback, public_key, public_key(rsa(Modulus, Exponent, -, -, -, -, -, -)), Key)
; memberchk(element(DS:'DSAKeyValue', _, _DSAKeyValue), KeyInfo)
-> throw(error(not_implemented(dsa_key), _)) % FIXME: Not implemented
; existence_error(usable_key_value, KeyValue)
).
resolve_key(KeyInfo, Key, KeyCallback, _Options):-
% X509Data.
DS = ns(_, 'http://www.w3.org/2000/09/xmldsig#'),
memberchk(element(DS:'X509Data', _, X509Data), KeyInfo),
memberchk(element(DS:'X509Certificate', _, [X509Certificate]), X509Data),
!,
load_certificate_from_base64_string(X509Certificate, Certificate),
call(KeyCallback, certificate, Certificate, Key).
resolve_key(KeyInfo, _Key, _KeyCallback, _Options):-
% PGPData. FIXME: Not implemented
DS = ns(_, 'http://www.w3.org/2000/09/xmldsig#'),
memberchk(element(DS:'PGPData', _KeyAttributes, _PGPData), KeyInfo),
!,
throw(not_implemented).
resolve_key(KeyInfo, _Key, _KeyCallback, _Options):-
% SPKIData. FIXME: Not implemented
DS = ns(_, 'http://www.w3.org/2000/09/xmldsig#'),
memberchk(element(DS:'SPKIData', _KeyAttributes, _SPKIData), KeyInfo),
!,
throw(not_implemented).
resolve_key(KeyInfo, _Key, _KeyCallback, _Options):-
% MgmtData. FIXME: Not implemented
DS = ns(_, 'http://www.w3.org/2000/09/xmldsig#'),
memberchk(element(DS:'MgmtData', _KeyAttributes, _SPKIData), KeyInfo),
!,
throw(not_implemented).
resolve_key(Info, _, _, _):-
% The XML-ENC standard allows for arbitrary other means of transmitting keys in application-specific
% protocols. This is not supported here, though. In the future a callback could be provided in Options
% to obtain the key information from a KeyInfo structure.
existence_error(usable_key, Info).
base64_to_hex(Base64, Hex):-
base64(Raw, Base64),
atom_codes(Raw, Codes),
hex_bytes(Hex0, Codes),
string_upper(Hex0, Hex).
determine_encryption_algorithm(EncryptedData, Algorithm, IVSize):-
XENC = ns(_, 'http://www.w3.org/2001/04/xmlenc#'),
( memberchk(element(XENC:'EncryptionMethod', EncryptionMethodAttributes, _), EncryptedData)
-> % This is a mandatory attribute
memberchk('Algorithm'=XMLAlgorithm, EncryptionMethodAttributes),
( ssl_algorithm(XMLAlgorithm, Algorithm, IVSize)
-> true
; domain_error(block_cipher, XMLAlgorithm)
)
% In theory the EncryptionMethod is optional. In pracitse though, if the method is not supplied we
% cannot decrypt the data. In the future we could support encryption_algorithm/1 as an option to
% decrypt_element/3 but for now raise an exception
; existence_error(encryption_method, EncryptedData)
).
base64_element([CipherValueElement], CipherValue):-
atom_codes(CipherValueElement, Base64Codes),
delete_newlines(Base64Codes, TrimmedCodes),
string_codes(Trimmed, TrimmedCodes),
base64(CipherValue, Trimmed).
delete_newlines([], []):- !.
delete_newlines([13|As], B):- !, delete_newlines(As, B).
delete_newlines([10|As], B):- !, delete_newlines(As, B).
delete_newlines([A|As], [A|B]):- !, delete_newlines(As, B).
%! load_certificate_from_base64_string(+String, -Certificate) is det.
%
% Loads a certificate from a string, adding newlines and header
% where appropriate so that OpenSSL 1.0.1+ will be able to parse it
load_certificate_from_base64_string(UnnormalizedData, Certificate):-
normalize_space(codes(Codes), UnnormalizedData),
% Break into 64-byte chunks
chunk_certificate(Codes, Chunks),
atomics_to_string(["-----BEGIN CERTIFICATE-----"|Chunks], '\n', CompleteCertificate),
setup_call_cleanup(open_string(CompleteCertificate, StringStream),
load_certificate(StringStream, Certificate),
close(StringStream)).
chunk_certificate(Codes, [Chunk|Chunks]):-
length(ChunkCodes, 64),
append(ChunkCodes, Rest, Codes),
!,
string_codes(Chunk, ChunkCodes),
chunk_certificate(Rest, Chunks).
chunk_certificate([], ["-----END CERTIFICATE-----\n"]):- !.
chunk_certificate(LastCodes, [LastChunk, "-----END CERTIFICATE-----\n"]):-
string_codes(LastChunk, LastCodes).