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Clarify documentation on encrypted files

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Explicitly state how QPDF handles empty passwords when writing files.
Apparently some libraries treat the empty string as the owner password
as an instruction to generate a random password.
This commit is contained in:
Jay Berkenbilt 2013-03-11 11:28:11 -04:00
parent f13558dddb
commit 9d4f52c014
1 changed files with 14 additions and 7 deletions
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21
include/qpdf/QPDFWriter.hh
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@ -219,13 +219,20 @@ class QPDFWriter
QPDF_DLL
void copyEncryptionParameters(QPDF&);
// Set up for encrypted output. Disables stream prefiltering and
// content normalization. Note that setting R2 encryption
// parameters sets the PDF version to at least 1.3, setting R3
// encryption parameters pushes the PDF version number to at least
// 1.4, setting R4 parameters pushes the version to at least 1.5,
// or if AES is used, 1.6, and setting R5 or R6 parameters pushes
// the version to at least 1.7 with extension level 3.
// Set up for encrypted output. User and owner password both must
// be specified. Either or both may be the empty string. Note
// that qpdf does not apply any special treatment to the empty
// string, which makes it possible to create encrypted files with
// empty owner passwords and non-empty user passwords or with the
// same password for both user and owner. Some PDF reading
// products don't handle such files very well. Enabling
// encryption disables stream prefiltering and content
// normalization. Note that setting R2 encryption parameters sets
// the PDF version to at least 1.3, setting R3 encryption
// parameters pushes the PDF version number to at least 1.4,
// setting R4 parameters pushes the version to at least 1.5, or if
// AES is used, 1.6, and setting R5 or R6 parameters pushes the
// version to at least 1.7 with extension level 3.
QPDF_DLL
void setR2EncryptionParameters(
char const* user_password, char const* owner_password,