Learn crypto from Buu (Zhou Geng)

First of all, a good article ：https://www.cnblogs.com/ruoli-s/p/14206145.html, Simple decryption of this article can . And this one. ：https://blog.csdn.net/qq_40836553/article/details/79383488

MD5

Decrypt website ！

MD5 It's the message digest algorithm , It is irreversible . therefore , If you want to decrypt, you can only get it by decrypting with huge profits MD5 String before encryption .

MD5 The full name is Message-Digest Algorithm, Belong to Hash One of the most important algorithms , With single encryption 、 The encryption result is unique 、 Good safety performance and other advantages .MD5 With 512 Bit grouping to process the input information , And each group is divided into 16 individual 32 Group the seats , After a series of treatment , The output of the algorithm consists of four 32 Bit grouping composition , Put these four 32 After the concatenation of bit groups, a 128 Bit hash value .

Link to the original text ：https://blog.csdn.net/m0_69916115/article/details/124433070

Base

Extract from the article ：

base16 features ： Capital (A-Z) And number (0-9), no need ‘=’.
base58 features ： comparison Base64,Base58 Do not use numbers "0", Capital letters "O", Capital letters "I", And lowercase letters "l", as well as "+“ and ”/" Symbol , The most important thing is that there will be no ’='.
base85 features ： The characteristic is that there are many strange characters , But it's hard to have an equal sign

base91 features ： from 91 Characters （0-9,a-z,A-Z,!#$%&()*+,./:;<=>[email protected][]^_`{|}~”） form , Chinese encryption is not supported .
base32: features ： Capital (A-Z) And number (2-7), discontent 5 Multiple , use ‘=’ A filling .
base64: features ： Case letters （A-Z,a-z） And number （0-9） And special symbols ‘+’,‘/’, discontent 3 Multiple , use ‘=’ A filling .

base100 features ： a pile Emoji expression

Url code

%66%6c%61%67%7b%61%6e%64%20%31%3d%31%7d// Look at the format 

url Coding is also called percent sign coding ,. Any special character （ Those are not simple seven ASCII, Such as Chinese characters ） Will be displayed in percentiles % Hexadecimal encoding , Of course, it also includes elephants =,&;, and % These special characters . Actually url A code is a character ascii The hexadecimal of the code . But there are some changes , You need to add “%”.

BUUCTF Watch me spin

ROT13（ Turn around 13 position ,rotate by 13 places, Sometimes a hyphen in the middle is called ROT-13） It's a simple replacement password .ROT13（ Turn around 13 position ,rotate by 13 places, Sometimes a hyphen in the middle is called ROT-13） It's a simple replacement password .

Caesar decrypts and grasps the offset

Variation Caesar

The prompt is obvious , It has the nature of Caesar , It's different

Compare up and down , Find common ground ,ASCII surface , By observing the rules of the first five characters , It can be found that the encrypted ciphertext is f-5=a,l-f=6, Between every two corresponding characters ASCII The difference increases gradually , Increment of 1

ciphertext = 'afZ_r9VYfScOeO_UL^RWUc'
j = 5
for i in ciphertext:
    print(chr(ord(i) + j), end='')
    j += 1

Internet search , I haven't seen this function before , This can also be written by yourself , It's not hard to ！

Moss

Tools
Direct translation is also OK

password

This question is a little off the mark ,,,,flag Add birthday to initials （ Look at that idiot who named the password like this !）

Quoted-printable

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Quoted-printable It can be translated into “ Printable character reference code ”、“ Use the encoding of printable characters ”, We receive mail , Check the original information of the letter , You often see this type of coding ！ It is a Multipurpose Internet mail extension （MIME) A way of implementation . among MIME It's an Internet standard , It extends the e-mail standard , Committed to enabling it to support non ASCII character 、 Binary format attachments and other mail messages in various formats .

principle ： One 8 The byte value of bit can be encoded as 3 Characters ： An equal sign ”=” Followed by two hexadecimal digits (0–9 or A–F) Represents the value of the byte . All printable ASCII character ( The range of decimal values is 33 To 126) You can use ASCII Character encoding to directly represent , But the equal sign ”=”( The decimal value is 61) You can't directly express .ASCII Horizontal tab for (tab) Match with space , Decimal system 9 and 32, If it doesn't appear at the end of the line, you can use it ASCII Character encoding directly represents . If these two characters appear at the end of the line , must QP The code is expressed as ”=09″ (tab) or ”=20″ (space).
If the data contains a meaningful end of line flag , Must be converted to ASCII enter (CR) Line break (LF) Sequence , You can't use the original ASCII Characters cannot be used either QP Coded ”=” Escape character sequence . contrary , If the byte value 13 And 10 There are other meanings that are not the end of the line , They must QP Encoded as =0D And =0A.
quoted-printable The length of each row of encoded data cannot exceed 76 Characters . To meet this requirement without changing the encoded text , stay QP Add a soft wrap at the end of each line of the encoding result (soft line break). That is, add a... At the end of each line ”=”, But it will not appear in the decoded text .

Rabbit

Decryption tools ,U2fsd The beginning is rabbit encryption

Rabbit Is a high-speed stream cipher , On 2003 In FSE It was first put forward in the seminar .Rabbit Use one 128 Bit key and a 64 Bit initialization vector . The core component of the encryption algorithm is a bit stream generator , The stream generator encrypts each iteration 128 Message bits .Rabbit It's also a symmetric encryption algorithm .

Other … I can't find it .