181 lines
7.0 KiB
Plaintext
181 lines
7.0 KiB
Plaintext
=pod
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=encoding utf8
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=head1 NAME
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passphrase-encoding
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- How diverse parts of OpenSSL treat pass phrases character encoding
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=head1 DESCRIPTION
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In a modern world with all sorts of character encodings, the treatment of pass
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phrases has become increasingly complex.
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This manual page attempts to give an overview over how this problem is
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currently addressed in different parts of the OpenSSL library.
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=head2 The general case
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The OpenSSL library doesn't treat pass phrases in any special way as a general
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rule, and trusts the application or user to choose a suitable character set
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and stick to that throughout the lifetime of affected objects.
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This means that for an object that was encrypted using a pass phrase encoded in
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ISO-8859-1, that object needs to be decrypted using a pass phrase encoded in
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ISO-8859-1.
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Using the wrong encoding is expected to cause a decryption failure.
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=head2 PKCS#12
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PKCS#12 is a bit different regarding pass phrase encoding.
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The standard stipulates that the pass phrase shall be encoded as an ASN.1
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BMPString, which consists of the code points of the basic multilingual plane,
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encoded in big endian (UCS-2 BE).
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OpenSSL tries to adapt to this requirements in one of the following manners:
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=over 4
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=item 1.
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Treats the received pass phrase as UTF-8 encoded and tries to re-encode it to
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UTF-16 (which is the same as UCS-2 for characters U+0000 to U+D7FF and U+E000
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to U+FFFF, but becomes an expansion for any other character), or failing that,
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proceeds with step 2.
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=item 2.
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Assumes that the pass phrase is encoded in ASCII or ISO-8859-1 and
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opportunistically prepends each byte with a zero byte to obtain the UCS-2
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encoding of the characters, which it stores as a BMPString.
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Note that since there is no check of your locale, this may produce UCS-2 /
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UTF-16 characters that do not correspond to the original pass phrase characters
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for other character sets, such as any ISO-8859-X encoding other than
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ISO-8859-1 (or for Windows, CP 1252 with exception for the extra "graphical"
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characters in the 0x80-0x9F range).
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=back
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OpenSSL versions older than 1.1.0 do variant 2 only, and that is the reason why
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OpenSSL still does this, to be able to read files produced with older versions.
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It should be noted that this approach isn't entirely fault free.
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A pass phrase encoded in ISO-8859-2 could very well have a sequence such as
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0xC3 0xAF (which is the two characters "LATIN CAPITAL LETTER A WITH BREVE"
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and "LATIN CAPITAL LETTER Z WITH DOT ABOVE" in ISO-8859-2 encoding), but would
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be misinterpreted as the perfectly valid UTF-8 encoded code point U+00EF (LATIN
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SMALL LETTER I WITH DIAERESIS) I<if the pass phrase doesn't contain anything that
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would be invalid UTF-8>.
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A pass phrase that contains this kind of byte sequence will give a different
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outcome in OpenSSL 1.1.0 and newer than in OpenSSL older than 1.1.0.
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0x00 0xC3 0x00 0xAF # OpenSSL older than 1.1.0
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0x00 0xEF # OpenSSL 1.1.0 and newer
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On the same accord, anything encoded in UTF-8 that was given to OpenSSL older
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than 1.1.0 was misinterpreted as ISO-8859-1 sequences.
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=head2 OSSL_STORE
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L<ossl_store(7)> acts as a general interface to access all kinds of objects,
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potentially protected with a pass phrase, a PIN or something else.
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This API stipulates that pass phrases should be UTF-8 encoded, and that any
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other pass phrase encoding may give undefined results.
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This API relies on the application to ensure UTF-8 encoding, and doesn't check
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that this is the case, so what it gets, it will also pass to the underlying
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loader.
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=head1 RECOMMENDATIONS
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This section assumes that you know what pass phrase was used for encryption,
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but that it may have been encoded in a different character encoding than the
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one used by your current input method.
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For example, the pass phrase may have been used at a time when your default
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encoding was ISO-8859-1 (i.e. "naïve" resulting in the byte sequence 0x6E 0x61
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0xEF 0x76 0x65), and you're now in an environment where your default encoding
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is UTF-8 (i.e. "naïve" resulting in the byte sequence 0x6E 0x61 0xC3 0xAF 0x76
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0x65).
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Whenever it's mentioned that you should use a certain character encoding, it
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should be understood that you either change the input method to use the
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mentioned encoding when you type in your pass phrase, or use some suitable tool
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to convert your pass phrase from your default encoding to the target encoding.
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Also note that the sub-sections below discuss human readable pass phrases.
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This is particularly relevant for PKCS#12 objects, where human readable pass
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phrases are assumed.
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For other objects, it's as legitimate to use any byte sequence (such as a
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sequence of bytes from `/dev/urandom` that's been saved away), which makes any
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character encoding discussion irrelevant; in such cases, simply use the same
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byte sequence as it is.
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=head2 Creating new objects
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For creating new pass phrase protected objects, make sure the pass phrase is
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encoded using UTF-8.
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This is default on most modern Unixes, but may involve an effort on other
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platforms.
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Specifically for Windows, setting the environment variable
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C<OPENSSL_WIN32_UTF8> will have anything entered on [Windows] console prompt
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converted to UTF-8 (command line and separately prompted pass phrases alike).
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=head2 Opening existing objects
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For opening pass phrase protected objects where you know what character
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encoding was used for the encryption pass phrase, make sure to use the same
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encoding again.
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For opening pass phrase protected objects where the character encoding that was
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used is unknown, or where the producing application is unknown, try one of the
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following:
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=over 4
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=item 1.
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Try the pass phrase that you have as it is in the character encoding of your
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environment.
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It's possible that its byte sequence is exactly right.
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=item 2.
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Convert the pass phrase to UTF-8 and try with the result.
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Specifically with PKCS#12, this should open up any object that was created
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according to the specification.
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=item 3.
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Do a naïve (i.e. purely mathematical) ISO-8859-1 to UTF-8 conversion and try
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with the result.
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This differs from the previous attempt because ISO-8859-1 maps directly to
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U+0000 to U+00FF, which other non-UTF-8 character sets do not.
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This also takes care of the case when a UTF-8 encoded string was used with
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OpenSSL older than 1.1.0.
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(for example, C<ï>, which is 0xC3 0xAF when encoded in UTF-8, would become 0xC3
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0x83 0xC2 0xAF when re-encoded in the naïve manner.
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The conversion to BMPString would then yield 0x00 0xC3 0x00 0xA4 0x00 0x00, the
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erroneous/non-compliant encoding used by OpenSSL older than 1.1.0)
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=back
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=head1 SEE ALSO
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L<evp(7)>,
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L<ossl_store(7)>,
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L<EVP_BytesToKey(3)>, L<EVP_DecryptInit(3)>,
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L<PEM_do_header(3)>,
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L<PKCS12_parse(3)>, L<PKCS12_newpass(3)>,
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L<d2i_PKCS8PrivateKey_bio(3)>
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=head1 COPYRIGHT
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Copyright 2018-2020 The OpenSSL Project Authors. All Rights Reserved.
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Licensed under the OpenSSL license (the "License"). You may not use
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this file except in compliance with the License. You can obtain a copy
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in the file LICENSE in the source distribution or at
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L<https://www.openssl.org/source/license.html>.
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=cut
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