yafu用於自動整數因式分解，在RSA中，當p、q的取值差異過大或過於相近的時候，使用yafu可以快速的把n值分解出p、q值，原理是使用Fermat方法與Pollard rho方法等。
再摘錄官方的一段簡介（又懶得翻譯了）。
YAFU (with assistance from other free software) uses the most powerful modern algorithms (and implementations of them) to factor input integers in a completely automated way. The automation within YAFU is state-of-the-art, combining factorization algorithms in an intelligent and adaptive methodology that minimizes the time to find the factors of arbitrary input integers. Most algorithm implementations are multi-threaded, allowing YAFU to fully utilize multi- or many-core processors (including SNFS, GNFS, SIQS, and ECM). YAFU is primarily a command-line driven tool. You provide the number to factor and, via screen output and log files, YAFU will provide you the factors. There is also an interactive environment similar to MATLAB or PARI/GP, where you can type commands and store results. YAFU is very customizable, through the optional use of many many command line parameters and a very capable expression interpreter.
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1. windows安裝
https://sourceforge.net/projects/yafu/
現在最新版本是1.34版本，下載后解壓即可。
解壓后有yafu-Win32.exe和yafu-x64.exe，推薦使用64位的。
2. linux安裝
上面壓縮包里有一個yafu的elf文件，可以在一些linux上運行，由於是靜態編譯的，在一些系統上想要使用yafu就得重新編譯。
3. linux編譯安裝
參考了sherlly的文章，然后測試、整合成腳本。
apt-get update apt-get install gcc m4 zlib1g-dev make -y mkdir -p $HOME/src # install gmp cd $HOME/src v=6.1.2 wget https://gmplib.org/download/gmp/gmp-${v}.tar.bz2 tar -jxvf gmp-${v}.tar.bz2 && mv gmp-${v} gmp && cd gmp ./configure make && make check && make install # install gmp-ecm cd $HOME/src v=6.2 wget https://gforge.inria.fr/frs/download.php/file/4663/ecm-${v}.tar.gz tar zxvf ecm-${v}.tar.gz && mv ecm-${v} gmp-ecm && cd gmp-ecm # replace __GMP_BITS_PER_MP_LIMB with GMP_LIMB_BITS x='__GMP_BITS_PER_MP_LIMB';y='GMP_LIMB_BITS';sed -i "s#${x}#${y}#g" `grep ${x} -rl .` ./configure --with-gmp=/usr/local make && make install # install msieve cd $HOME/src v1=1.52 v2=152 wget http://downloads.sourceforge.net/project/msieve/msieve/Msieve%20v${v1}/msieve${v2}.tar.gz tar zxvf msieve${v2}.tar.gz && mv msieve-${v1} msieve && cd msieve make all # install yafu cd $HOME/src git clone https://github.com/DarkenCode/yafu cd yafu # modify Makefile sed -i 's#INC = -I. -Iinclude#& -Itop/aprcl#;s#gmp/include#gmp#g;s#gmp/lib/linux/x86_64#gmp/.libs#; s#gmp-ecm/include/linux#gmp-ecm#g;s#gmp-ecm/lib/linux/x86_64#gmp-ecm/.libs#; s#msieve/lib/linux/x86_64#msieve#;122i LIBS+= -lc -lz' Makefile # comment sed -i 's#printf("setting prime roots#//&#g;s#printf("medsieve#//&#g;s#printf("lpsieve#//&#g; s#printf("scan p#//&#g;s#printf("next B#//&#g;s#printf("next roots#//&#g' factor/qs/SIQS.c make x86_64 NFS=1
4. yafu使用方法
使用cmd進入yafu的解壓目錄（為了方便的話，自己可以把該目錄加入到環境變量。）
輸入yafu-x64進入命令行
最常用的命令是factor(n)，將n值分解
如分解23333333333333
factor(23333333333333)
很快得到：
fac: factoring 23333333333333 fac: using pretesting plan: normal fac: no tune info: using qs/gnfs crossover of 95 digits div: primes less than 10000 fmt: 1000000 iterations Total factoring time = 0.2805 seconds ***factors found*** P2 = 31 P12 = 752688172043 ans = 1
5. 使用yafu的時候遇到mismatched parens
這是因為在命令行里不支持過長的位數，所以我們只要把n的值從文件中去讀取即可。
查看yafu的幫助：
yafu-x64.exe help
新建一個文件pcat.txt，內容里寫上n的值，如：
966808932627497190635859236054960349099463975227350564265384373280336699853387254070662881265937565163000758606154308757944030571837175048514574473061401566330836334647176655282619268592560172726526643074499534129878217409046045533656897050117438496357231575999185527675071002803951800635220029015932007465117818739948903750200830856115668691007706836952244842719419452946259275251773298338162389930518838272704908887016474007051397194588396039111216708866214614779627566959335170676055025850932631053641576566165694121420546081043285806783239296799795655191121966377590175780618944910532816988143056757054052679968538901460893571204904394975714081055455240523895653305315517745729334114549756695334171142876080477105070409544777981602152762154610738540163796164295222810243309051503090866674634440359226192530724635477051576515179864461174911975667162597286769079380660782647952944808596310476973939156187472076952935728249061137481887589103973591082872988641958270285169650803792395556363304056290077801453980822097583574309682935697260204862756923865556397686696854239564541407185709940107806536773160263764483443859425726953142964148216209968437587044617613518058779287167853349364533716458676066734216877566181514607693882375533
注意：最后面一定要換行，不然會出現eof; done processing batchfile
然后運行命令為
yafu-x64 "factor(@)" -batchfile pcat.txt
很快得到：
***factors found*** PRP617 = 31093551302922880999883020803665536616272147022877428745314830867519351013248914244880101094365815998050115415308439610066700139164376274980650005150267949853671653233491784289493988946869396093730966325659249796545878080119206283512342980854475734097108975670778836003822789405498941374798016753689377992355122774401780930185598458240894362246194248623911382284169677595864501475308194644140602272961699230282993020507668939980205079239221924230430230318076991507619960330144745307022538024878444458717587446601559546292026245318907293584609320115374632235270795633933755350928537598242214216674496409625928997877221 PRP617 = 31093551302922880999883020803665536616272147022877428745314830867519351013248914244880101094365815998050115415308439610066700139164376274980650005150267949853671653233491784289493988946869396093730966325659249796545878080119206283512342980854475734097108975670778836003822789405498941374798016753689377992355122774401780930185598458240894362246194248623911382284169677595864501475308194644140602272961699230282993020507668939980205079239221924230430230318076991507619960330144745307022538024878444458717587446601559546292026245318907293584609320115374632235270795633933755350928537598242214216674496409625928797450473 ans = 1
注意：運行后，pcat.txt就會消失了。