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Diffstat (limited to 'secure/lib/libcrypto/man/des_modes.3')
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diff --git a/secure/lib/libcrypto/man/des_modes.3 b/secure/lib/libcrypto/man/des_modes.3 new file mode 100644 index 0000000..8b2ac65 --- /dev/null +++ b/secure/lib/libcrypto/man/des_modes.3 @@ -0,0 +1,290 @@ +.\" Automatically generated by Pod::Man version 1.15 +.\" Thu May 9 13:19:11 2002 +.\" +.\" Standard preamble: +.\" ====================================================================== +.de Sh \" Subsection heading +.br +.if t .Sp +.ne 5 +.PP +\fB\\$1\fR +.PP +.. +.de Sp \" Vertical space (when we can't use .PP) +.if t .sp .5v +.if n .sp +.. +.de Ip \" List item +.br +.ie \\n(.$>=3 .ne \\$3 +.el .ne 3 +.IP "\\$1" \\$2 +.. +.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. | will give a +.\" real vertical bar. \*(C+ will give a nicer C++. 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Those +are used for using block ciphers in a way similar to stream ciphers, among +other things. +.SH "OVERVIEW" +.IX Header "OVERVIEW" +.Sh "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. +.Sh "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\s0 \s-1CBC\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. +.Sh "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. +.Sh "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. +.Sh "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 key space to 55 bit's but it +requires 2^56 blocks of memory. +.Ip "\(bu" 2 +If all 3 keys are the same, this is effectively the same as normal +ecb mode. +.Sh "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" +blowfish(3), des(3), idea(3), +rc2(3) |
