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diff --git a/usr/man/man7/des_modes.7 b/usr/man/man7/des_modes.7 new file mode 100755 index 000000000..5da259f66 --- /dev/null +++ b/usr/man/man7/des_modes.7 @@ -0,0 +1,288 @@ +.\" Automatically generated by Pod::Man 2.28 (Pod::Simple 3.28) +.\" +.\" Standard preamble: +.\" ======================================================================== +.de Sp \" Vertical space (when we can't use .PP) +.if t .sp .5v +.if n .sp +.. +.de Vb \" Begin verbatim text +.ft CW +.nf +.ne \\$1 +.. +.de Ve \" End verbatim text +.ft R +.fi +.. +.\" Set up some character translations and predefined strings. \*(-- will +.\" give an unbreakable dash, \*(PI will give pi, \*(L" will give a left +.\" double quote, and \*(R" will give a right double quote. \*(C+ will +.\" give a nicer C++. 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Always turn off hyphenation; it makes +.\" way too many mistakes in technical documents. +.if n .ad l +.nh +.SH "NAME" +des_modes \- the variants of DES and other crypto algorithms of OpenSSL +.SH "DESCRIPTION" +.IX Header "DESCRIPTION" +Several crypto algorithms for OpenSSL can be used in a number of modes. Those +are used for using block ciphers in a way similar to stream ciphers, among +other things. +.SH "OVERVIEW" +.IX Header "OVERVIEW" +.SS "Electronic Codebook Mode (\s-1ECB\s0)" +.IX Subsection "Electronic Codebook Mode (ECB)" +Normally, this is found as the function \fIalgorithm\fR\fI_ecb_encrypt()\fR. +.IP "\(bu" 2 +64 bits are enciphered at a time. +.IP "\(bu" 2 +The order of the blocks can be rearranged without detection. +.IP "\(bu" 2 +The same plaintext block always produces the same ciphertext block +(for the same key) making it vulnerable to a 'dictionary attack'. +.IP "\(bu" 2 +An error will only affect one ciphertext block. +.SS "Cipher Block Chaining Mode (\s-1CBC\s0)" +.IX Subsection "Cipher Block Chaining Mode (CBC)" +Normally, this is found as the function \fIalgorithm\fR\fI_cbc_encrypt()\fR. +Be aware that \fIdes_cbc_encrypt()\fR is not really \s-1DES CBC \s0(it does +not update the \s-1IV\s0); use \fIdes_ncbc_encrypt()\fR instead. +.IP "\(bu" 2 +a multiple of 64 bits are enciphered at a time. +.IP "\(bu" 2 +The \s-1CBC\s0 mode produces the same ciphertext whenever the same +plaintext is encrypted using the same key and starting variable. +.IP "\(bu" 2 +The chaining operation makes the ciphertext blocks dependent on the +current and all preceding plaintext blocks and therefore blocks can not +be rearranged. +.IP "\(bu" 2 +The use of different starting variables prevents the same plaintext +enciphering to the same ciphertext. +.IP "\(bu" 2 +An error will affect the current and the following ciphertext blocks. +.SS "Cipher Feedback Mode (\s-1CFB\s0)" +.IX Subsection "Cipher Feedback Mode (CFB)" +Normally, this is found as the function \fIalgorithm\fR\fI_cfb_encrypt()\fR. +.IP "\(bu" 2 +a number of bits (j) <= 64 are enciphered at a time. +.IP "\(bu" 2 +The \s-1CFB\s0 mode produces the same ciphertext whenever the same +plaintext is encrypted using the same key and starting variable. +.IP "\(bu" 2 +The chaining operation makes the ciphertext variables dependent on the +current and all preceding variables and therefore j\-bit variables are +chained together and can not be rearranged. +.IP "\(bu" 2 +The use of different starting variables prevents the same plaintext +enciphering to the same ciphertext. +.IP "\(bu" 2 +The strength of the \s-1CFB\s0 mode depends on the size of k (maximal if +j == k). In my implementation this is always the case. +.IP "\(bu" 2 +Selection of a small value for j will require more cycles through +the encipherment algorithm per unit of plaintext and thus cause +greater processing overheads. +.IP "\(bu" 2 +Only multiples of j bits can be enciphered. +.IP "\(bu" 2 +An error will affect the current and the following ciphertext variables. +.SS "Output Feedback Mode (\s-1OFB\s0)" +.IX Subsection "Output Feedback Mode (OFB)" +Normally, this is found as the function \fIalgorithm\fR\fI_ofb_encrypt()\fR. +.IP "\(bu" 2 +a number of bits (j) <= 64 are enciphered at a time. +.IP "\(bu" 2 +The \s-1OFB\s0 mode produces the same ciphertext whenever the same +plaintext enciphered using the same key and starting variable. More +over, in the \s-1OFB\s0 mode the same key stream is produced when the same +key and start variable are used. Consequently, for security reasons +a specific start variable should be used only once for a given key. +.IP "\(bu" 2 +The absence of chaining makes the \s-1OFB\s0 more vulnerable to specific attacks. +.IP "\(bu" 2 +The use of different start variables values prevents the same +plaintext enciphering to the same ciphertext, by producing different +key streams. +.IP "\(bu" 2 +Selection of a small value for j will require more cycles through +the encipherment algorithm per unit of plaintext and thus cause +greater processing overheads. +.IP "\(bu" 2 +Only multiples of j bits can be enciphered. +.IP "\(bu" 2 +\&\s-1OFB\s0 mode of operation does not extend ciphertext errors in the +resultant plaintext output. Every bit error in the ciphertext causes +only one bit to be in error in the deciphered plaintext. +.IP "\(bu" 2 +\&\s-1OFB\s0 mode is not self-synchronizing. If the two operation of +encipherment and decipherment get out of synchronism, the system needs +to be re-initialized. +.IP "\(bu" 2 +Each re-initialization should use a value of the start variable +different from the start variable values used before with the same +key. The reason for this is that an identical bit stream would be +produced each time from the same parameters. This would be +susceptible to a 'known plaintext' attack. +.SS "Triple \s-1ECB\s0 Mode" +.IX Subsection "Triple ECB Mode" +Normally, this is found as the function \fIalgorithm\fR\fI_ecb3_encrypt()\fR. +.IP "\(bu" 2 +Encrypt with key1, decrypt with key2 and encrypt with key3 again. +.IP "\(bu" 2 +As for \s-1ECB\s0 encryption but increases the key length to 168 bits. +There are theoretic attacks that can be used that make the effective +key length 112 bits, but this attack also requires 2^56 blocks of +memory, not very likely, even for the \s-1NSA.\s0 +.IP "\(bu" 2 +If both keys are the same it is equivalent to encrypting once with +just one key. +.IP "\(bu" 2 +If the first and last key are the same, the key length is 112 bits. +There are attacks that could reduce the effective key strength +to only slightly more than 56 bits, but these require a lot of memory. +.IP "\(bu" 2 +If all 3 keys are the same, this is effectively the same as normal +ecb mode. +.SS "Triple \s-1CBC\s0 Mode" +.IX Subsection "Triple CBC Mode" +Normally, this is found as the function \fIalgorithm\fR\fI_ede3_cbc_encrypt()\fR. +.IP "\(bu" 2 +Encrypt with key1, decrypt with key2 and then encrypt with key3. +.IP "\(bu" 2 +As for \s-1CBC\s0 encryption but increases the key length to 168 bits with +the same restrictions as for triple ecb mode. +.SH "NOTES" +.IX Header "NOTES" +This text was been written in large parts by Eric Young in his original +documentation for SSLeay, the predecessor of OpenSSL. In turn, he attributed +it to: +.PP +.Vb 5 +\& AS 2805.5.2 +\& Australian Standard +\& Electronic funds transfer \- Requirements for interfaces, +\& Part 5.2: Modes of operation for an n\-bit block cipher algorithm +\& Appendix A +.Ve +.SH "SEE ALSO" +.IX Header "SEE ALSO" +\&\fIblowfish\fR\|(3), \fIdes\fR\|(3), \fIidea\fR\|(3), +\&\fIrc2\fR\|(3) |