Modernise. Use libcrypto instead of libcipher for DES.
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svn2git
2020-12-20 02:59:44 +00:00
svn path=/head/; revision=115718
@ -2,7 +2,10 @@
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# $FreeBSD$
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PROG= bdes
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DPADD= ${LIBCIPHER}
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LDADD= -lcipher
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WARNS= 2
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DPADD= ${LIBCRYPTO}
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LDADD= -lcrypto
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.include <bsd.prog.mk>
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@ -40,7 +40,7 @@
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.Os
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.Sh NAME
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.Nm bdes
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.Nd "encrypt/decrypt using the Data Encryption Standard"
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.Nd "encrypt/decrypt using the Data Encryption Standard (DES)"
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.Sh SYNOPSIS
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.Nm
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.Op Fl abdp
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@ -61,22 +61,31 @@ including alternative cipher feedback mode and both authentication
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modes.
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The
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.Nm
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utility reads from the standard input and writes to the standard output.
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By default, the input is encrypted using cipher block chaining mode.
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Using the same key for encryption and decryption preserves plain text.
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utility reads from the standard input
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and writes to the standard output.
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By default,
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the input is encrypted
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using cipher block chaining (CBC) mode.
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Using the same key
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for encryption and decryption
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preserves plain text.
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.Pp
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All modes but the electronic code book mode require an initialization
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vector; if none is supplied, the zero vector is used.
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All modes but the electronic code book (ECB) mode
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require an initialization vector;
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if none is supplied,
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the zero vector is used.
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If no
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.Ar key
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is specified on the command line, the user is prompted for one (see
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is specified on the command line,
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the user is prompted for one (see
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.Xr getpass 3
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for more details).
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.Pp
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The options are as follows:
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.Bl -tag -width indent
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.It Fl a
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The key and initialization vector strings are to be taken as
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The key and initialization vector strings
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are to be taken as
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.Tn ASCII ,
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suppressing the special interpretation given to leading
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.Dq Li 0X ,
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@ -89,21 +98,22 @@ This flag applies to
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.Em both
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the key and initialization vector.
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.It Fl b
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Use electronic code book mode.
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Use ECB mode.
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.It Fl d
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Decrypt the input.
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.It Fl F Ar N
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Use
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.Ar N Ns \-bit
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alternative cipher feedback mode.
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alternative CFB mode.
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Currently
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.Ar N
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must be a multiple of 7 between 7 and 56 inclusive (this does not conform
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to the alternative CFB mode specification).
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must be a multiple of 7
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between 7 and 56 inclusive
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(this does not conform to the alternative CFB mode specification).
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.It Fl f Ar N
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Use
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.Ar N Ns \-bit
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cipher feedback mode.
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CFB mode.
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Currently
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.Ar N
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must be a multiple of 8 between 8 and 64 inclusive (this does not conform
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@ -120,130 +130,182 @@ The value of
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.Ar N
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must be between 1 and 64 inclusive; if
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.Ar N
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is not a multiple of 8, enough 0 bits will be added to pad the MAC length
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is not a multiple of 8,
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enough 0 bits will be added
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to pad the MAC length
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to the nearest multiple of 8.
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Only the MAC is output.
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MACs are only available in cipher block chaining mode or in cipher feedback
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mode.
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MACs are only available
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in CBC mode
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or in CFB mode.
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.It Fl o Ar N
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Use
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.Ar N Ns \-bit
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output feedback mode.
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ouput feedback (OFB) mode.
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Currently
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.Ar N
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must be a multiple of 8 between 8 and 64 inclusive (this does not conform
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to the OFB mode specification).
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.It Fl p
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Disable the resetting of the parity bit.
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This flag forces the parity bit of the key to be used as typed, rather than
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making each character be of odd parity.
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This flag forces
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the parity bit of the key
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to be used as typed,
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rather than making
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each character be of odd parity.
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It is used only if the key is given in
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.Tn ASCII .
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.It Fl v Ar vector
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Set the initialization vector to
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.Ar vector ;
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the vector is interpreted in the same way as the key.
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The vector is ignored in electronic codebook mode.
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The vector is ignored in ECB mode.
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.El
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.Pp
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The key and initialization vector are taken as sequences of
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The key and initialization vector
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are taken as sequences of
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.Tn ASCII
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characters which are then mapped into their bit representations.
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characters which are then mapped
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into their bit representations.
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If either begins with
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.Dq Li 0X
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or
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.Dq Li 0x ,
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that one is taken as a sequence of hexadecimal digits indicating the
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bit pattern;
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that one is taken
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as a sequence of hexadecimal digits
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indicating the bit pattern;
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if either begins with
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.Dq Li 0B
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or
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.Dq Li 0b ,
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that one is taken as a sequence of binary digits indicating the bit pattern.
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that one is taken
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as a sequence of binary digits
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indicating the bit pattern.
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In either case,
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only the leading 64 bits of the key or initialization vector
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only the leading 64 bits
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of the key or initialization vector
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are used,
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and if fewer than 64 bits are provided, enough 0 bits are appended
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and if fewer than 64 bits are provided,
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enough 0 bits are appended
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to pad the key to 64 bits.
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.Pp
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According to the
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.Tn DES
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standard, the low-order bit of each character in the
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key string is deleted.
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standard,
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the low-order bit of each character
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in the key string is deleted.
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Since most
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.Tn ASCII
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representations set the high-order bit to 0, simply
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deleting the low-order bit effectively reduces the size of the key space
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representations
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set the high-order bit to 0,
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simply deleting the low-order bit
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effectively reduces the size of the key space
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from 2^56 to 2^48 keys.
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To prevent this, the high-order bit must be a function depending in part
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upon the low-order bit; so, the high-order bit is set to whatever value
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gives odd parity.
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To prevent this,
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the high-order bit must be a function
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depending in part upon the low-order bit;
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so,
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the high-order bit is set
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to whatever value gives odd parity.
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This preserves the key space size.
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Note this resetting of the parity bit is
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.Em not
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done if the key is given in binary or hex, and can be disabled for
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done if the key
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is given in binary or hex,
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and can be disabled for
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.Tn ASCII
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keys as well.
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.Pp
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The
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.Tn DES
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is considered a very strong cryptosystem, and other than table lookup
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attacks, key search attacks, and Hellman's time-memory tradeoff (all of which
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are very expensive and time-consuming), no cryptanalytic methods for breaking
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the
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is considered a very strong cryptosystem,
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and other than table lookup attacks,
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key search attacks,
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and Hellman's time-memory tradeoff
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(all of which are very expensive and time-consuming),
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no cryptanalytic methods
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for breaking the
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.Tn DES
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are known in the open literature.
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No doubt the choice of keys and key security are the most vulnerable aspect
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of
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No doubt the choice of keys
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and key security
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are the most vulnerable aspect of
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.Nm .
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.Sh IMPLEMENTATION NOTES
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For implementors wishing to write software compatible with this program,
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For implementors wishing to write
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software compatible with this program,
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the following notes are provided.
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This software is believed to be compatible with the implementation of the
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data encryption standard distributed by Sun Microsystems, Inc.
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This software is believed
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to be compatible with the implementation
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of the data encryption standard
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distributed by Sun Microsystems, Inc.
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.Pp
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In the ECB and CBC modes, plaintext is encrypted in units of 64 bits (8 bytes,
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also called a block).
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To ensure that the plaintext file is encrypted correctly,
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In the ECB and CBC modes,
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plaintext is encrypted in units of 64 bits
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(8 bytes, also called a block).
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To ensure that the plaintext file
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is encrypted correctly,
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.Nm
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will (internally) append from 1 to 8 bytes, the last byte containing an
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integer stating how many bytes of that final block are from the plaintext
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file, and encrypt the resulting block.
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Hence, when decrypting, the last block may contain from 0 to 7 characters
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present in the plaintext file, and the last byte tells how many.
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Note that if during decryption the last byte of the file does not contain an
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integer between 0 and 7, either the file has been corrupted or an incorrect
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key has been given.
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A similar mechanism is used for the OFB and CFB modes, except that those
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simply require the length of the input to be a multiple of the mode size,
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and the final byte contains an integer between 0 and one less than the number
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will (internally) append from 1 to 8 bytes,
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the last byte containing an integer
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stating how many bytes of that final block
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are from the plaintext file,
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and encrypt the resulting block.
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Hence,
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when decrypting,
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the last block may contain from 0 to 7 characters
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present in the plaintext file,
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and the last byte tells how many.
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Note that if during decryption
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the last byte of the file
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does not contain an integer between 0 and 7,
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either the file has been corrupted
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or an incorrect key has been given.
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A similar mechanism is used
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for the OFB and CFB modes,
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except that those
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simply require the length of the input
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to be a multiple of the mode size,
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and the final byte contains an integer
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between 0 and one less than the number
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of bytes being used as the mode.
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(This was another reason that the mode size must be a multiple of 8 for those
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modes.)
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(This was another reason
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that the mode size must be
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a multiple of 8 for those modes.)
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.Pp
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Unlike Sun's implementation, unused bytes of that last block are not filled
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with random data, but instead contain what was in those byte positions in
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the preceding block.
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This is quicker and more portable, and does not weaken the encryption
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significantly.
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Unlike Sun's implementation,
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unused bytes of that last block
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are not filled with random data,
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but instead contain
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what was in those byte positions
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in the preceding block.
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This is quicker and more portable,
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and does not weaken the encryption significantly.
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.Pp
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If the key is entered in
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.Tn ASCII ,
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the parity bits of the key characters are set
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so that each key character is of odd parity.
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Unlike Sun's implementation, it is possible to enter binary or hexadecimal
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keys on the command line, and if this is done, the parity bits are
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the parity bits of the key characters
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are set so that each key character
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is of odd parity.
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Unlike Sun's implementation,
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it is possible to enter binary or hexadecimal
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keys on the command line,
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and if this is done,
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the parity bits are
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.Em not
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reset.
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This allows testing using arbitrary bit patterns as keys.
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This allows testing
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using arbitrary bit patterns as keys.
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.Pp
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The Sun implementation always uses an initialization vector of 0
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The Sun implementation
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always uses an initialization vector of 0
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(that is, all zeroes).
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By default,
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.Nm
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does too, but this may be changed from the command line.
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does too,
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but this may be changed
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from the command line.
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.Sh SEE ALSO
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.Xr crypt 3 ,
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.Xr getpass 3
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.Rs
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.%T "Data Encryption Standard"
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@ -289,21 +351,33 @@ There is a controversy raging over whether the
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.Tn DES
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will still be secure
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in a few years.
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The advent of special-purpose hardware could reduce the cost of any of the
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methods of attack named above so that they are no longer computationally
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infeasible.
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The advent of special-purpose hardware
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could reduce the cost of any of the
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methods of attack named above
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so that they are no longer
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computationally infeasible.
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.Pp
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As the key or key schedule is stored in memory, the encryption can be
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As the key or key schedule
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is stored in memory,
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the encryption can be
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compromised if memory is readable.
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Additionally, programs which display programs' arguments may compromise the
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key and initialization vector, if they are specified on the command line.
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Additionally,
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programs which display programs' arguments
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may compromise the key and initialization vector,
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if they are specified on the command line.
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To avoid this
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.Nm
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overwrites its arguments, however, the obvious race cannot currently be
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avoided.
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overwrites its arguments,
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however,
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the obvious race
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cannot currently be avoided.
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.Pp
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Certain specific keys should be avoided because they introduce potential
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weaknesses; these keys, called the
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Certain specific keys
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should be avoided
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because they introduce
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potential weaknesses;
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these keys,
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called the
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.Em weak
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and
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.Em semiweak
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@ -328,7 +402,8 @@ or
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.Pp
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This is inherent in the
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.Tn DES
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algorithm; see
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algorithm;
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see
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.Rs
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.%A Moore
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.%A Simmons
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