pdftk - What different options for password protection does PDF support? -


in pdftk can see 3 options:

1$ pdftk input.pdf output protected-userpw.pdf userpw very_secret 2$ pdftk input.pdf output protected-ownerpw.pdf ownerpw very_secret 3$ pdftk input.pdf input_pw very_secret output protected-input.pdf

when open protected-ownerpw.pdf , protected-input.pdf not asked password. protected-userpw.pdf gives expected result. what ownerpw , input_pw do?

i use qpdf create unprotected files protected ones. wonder if works. which password protection mechanisms pdf format support? , qpdf supports.

owner , user password different meanings

in pdf document can set security rights,

  • printing allowed
  • copying text allowed
  • filling out formfields allowed
  • ...

these flags inside document , pdf viewer, if obeys them or not.

when set owner password, user password automatically set empty. pdf file becoming still encrypted (all streams , strings saved in encrypted form), can decrypted empty password. can open pdf without password input, once opened have rights document, specified in security rights. maybe not allowed print document.

when set user , owner password opens pdf needs specify either owner or user password during opening. if has specified user password, security rights according security settings in pdf. if has used owner password, gets security rights granted.

pdf encryptions there many different encryption algorithms supported in pdf. rc4 or aes encryption key length of 40 128 , user defined algorithms, aren't covered inside pdf specification. in recent extenstions pdf 1.7 specification (extension level 3) aes 256 specified. in later extension there update specified, modified aes 256 bit , fixed theoretical security hole. several tools still have problem regarding these last extensions (but don't know qpdf). these extensions available inside normal pdf specification in iso specification of pdf 2.0, released today.


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