How does Microsoft SQL Server encrypt passwords? Undisclosed encryption functions

If you are interested in MSSQL user information, you may find the Master. DBO. sysxlogins stores user passwords. However, if the password field is not null, It is a bunch of binary files that cannot be understood. How is this password encrypted?
In fact, you only need to take a closer look at Master. DBO. sp_addlogin. You can see all the MSSQL Sp. Code Yes.
Let's take a look at how it works. Pay attention to this line of select @ passwd = pwdencrypt (@ passwd). After this, @ passwd will be encrypted. Let's also try it.
Declare @ clearpwd varchar (255)
Declare @ encryptedpwd varbinary (255)
Select @ clearpwd = 'test'
Select @ encryptedpwd = convert (varbinary (255), pwdencrypt (@ clearpwd ))
Select @ encryptedpwd
It looks good. It is indeed encrypted, but how can I restore it?

well, that's all. Password Encryption is one-way. You can use encrypted passwords to compare them.
continue to check the SP related to other users. You can find that there is password comparison in master. DBO. sp_password.
pwdcompare (@ old, password, (case when xstatus & 2048 = 2048 then 1 else 0 end)
ignore xstatus, which is a status mask, generally, we can use 0 directly.
declare @ clearpwd varchar (255)
declare @ encryptedpwd varbinary (255)
select @ clearpwd = 'test'
select @ encryptedpwd = convert (varbinary (255), pwdencrypt (@ clearpwd)
select pwdcompare (@ clearpwd, @ encryptedpwd, 0)
select pwdcompare ('errorpassword', @ encryptedp WD, 0)
so that we can use these two functions to encrypt our passwords. How about that?