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WriteProtection class

Write Protection. When the object is serialized out as xml, its qualified name is w:writeProtection.

System.Object
  DocumentFormat.OpenXml.OpenXmlElement
    DocumentFormat.OpenXml.OpenXmlLeafElement
      DocumentFormat.OpenXml.Wordprocessing.WriteProtection

Namespace:  DocumentFormat.OpenXml.Wordprocessing
Assembly:  DocumentFormat.OpenXml (in DocumentFormat.OpenXml.dll)

public class WriteProtection : OpenXmlLeafElement

[ISO/IEC 29500-1 1st Edition]

writeProtection (Write Protection)

This element specifies the write protection settings which have been applied to a WordprocessingML document. Write protection refers to a mode in which the document's contents cannot be edited, and the document cannot be resaved using the same file name. This setting is independent of the documentProtection (§17.15.1.29) element, but like document protection, this setting is not intended as a security feature and can be ignored.

When present, the write protection shall result in one of two write protection behaviors:

  • If the password attribute is present, or both attributes are omitted, then the application shall prompt for a password to exit write protection. If the supplied password does not match the hash value in this attribute, then write protection shall be enabled.

  • If only the recommended attribute is present, the application should provide user interface recommending that the user open this document in write protected state. If the user chooses to do so, the document shall be write protected, otherwise, it shall be opened fully editable.

If this element is omitted, then no write protection shall be applied to the current document.

[Example: Consider a WordprocessingML document that can be opened but only in a write protected state unless a password is provided, in which case the file would be opened in an editable state. This requirement would be specified using the following WordprocessingML in the document settings:

<w:writeProtection w:hash="9oN7nWkCAyEZib1RomSJTjmPpCY=" /> 

The writeProtection element is present which specifies that write protection must be turned on for this document. Since the password attribute is equal to 9oN7nWkCAyEZib1RomSJTjmPpCY= the given WordprocessingML document can only be opened in a write protected state unless a password which matches the hash value 9oN7nWkCAyEZib1RomSJTjmPpCY=is provided; in which case the file would be opened in an editable state. end example]

Parent Elements

settings (§17.15.1.78)

Attributes

Description

algorithmName (Cryptographic Algorithm Name)

Specifies the specific cryptographic hashing algorithm which shall be used along with the salt attribute and input password in order to compute the hash value.

The following values are reserved:

Value

Algorithm

MD2

Specifies that the MD2 algorithm, as defined by RFC 1319, shall be used.

[Note: It is recommended that applications should avoid using this algorithm to store new hash values, due to publically known breaks. end note]

MD4

Specifies that the MD4 algorithm, as defined by RFC 1320, shall be used.

[Note: It is recommended that applications should avoid using this algorithm to store new hash values, due to publically known breaks. end note]

MD5

Specifies that the MD5 algorithm, as defined by RFC 1321, shall be used.

[Note: It is recommended that applications should avoid using this algorithm to store new hash values, due to publically known breaks. end note]

RIPEMD-128

Specifies that the RIPEMD-128 algorithm, as defined by /IEC 10118-3:2004 shall be used.

[Note: It is recommended that applications should avoid using this algorithm to store new hash values, due to publically known breaks. end note]

RIPEMD-160

Specifies that the RIPEMD-160 algorithm, as defined by /IEC 10118-3:2004 shall be used.

SHA-1

Specifies that the SHA-1 algorithm, as defined by /IEC 10118-3:2004 shall be used.

SHA-256

Specifies that the SHA-256 algorithm, as defined by /IEC 10118-3:2004 shall be used.

SHA-384

Specifies that the SHA-384 algorithm, as defined by /IEC 10118-3:2004 shall be used.

SHA-512

Specifies that the SHA-512 algorithm, as defined by /IEC 10118-3:2004 shall be used.

WHIRLPOOL

Specifies that the WHIRLPOOL algorithm, as defined by /IEC 10118-3:2004 shall be used.

[Example: Consider an Office Open XML document with the following information stored in one of its protection elements:

< … algorithmName="SHA-1"   hashValue="9oN7nWkCAyEZib1RomSJTjmPpCY=" />

The algorithmName attribute value of “SHA-1” specifies that the SHA-1 hashing algorithm must be used to generate a hash from the user-defined password. end example]

The possible values for this attribute are defined by the ST_String simple type (§22.9.2.13).

hashValue (Password Hash Value)

Specifies the hash value for the password stored with this document. This value shall be compared with the resulting hash value after hashing the user-supplied password using the algorithm specified by the preceding attributes and parent XML element, and if the two values match, the protection shall no longer be enforced.

If this value is omitted, then the reservationPassword attribute shall contain the password hash for the workbook.

[Example: Consider an Office Open XML document with the following information stored in one of its protection elements:

<… AlgorithmName="SHA-1"  hashValue="9oN7nWkCAyEZib1RomSJTjmPpCY=" />

The hashValue attribute value of 9oN7nWkCAyEZib1RomSJTjmPpCY= specifies that the user-supplied password must be hashed using the pre-processing defined by the parent element (if any) followed by the SHA-1 algorithm (specified via the algorithmName attribute value of SHA-1) and that the resulting has value must be 9oN7nWkCAyEZib1RomSJTjmPpCY= for the protection to be disabled. end example]

The possible values for this attribute are defined by the W3C XML Schema base64Binary datatype.

recommended (Recommend Write Protection in User Interface)

Specifies that applications should provide user interface recommending that the user open this document in write protected state. If the user chooses to do so, the document shall be write protected, otherwise, it shall be opened fully editable.

If this attribute is omitted, then user interface recommending that the user open this document in write protected state should not be provided. If the password attribute is also specified, then this setting shall be ignored.

[Example: Consider a WordprocessingML document which specifies that applications must recommend write protection to this document. This requirement would be specified using the following WordprocessingML in the document settings:

<w:writeProtection w:recommended="true" /> 

The recommended attribute has a value of true specifying that the applications must hash any password provided, and if it matches this hash value, can only then halt enforcement of write protection. end example]

The possible values for this attribute are defined by the ST_OnOff simple type (§22.9.2.7).

saltValue (Salt Value for Password Verifier)

Specifies the salt which was prepended to the user-supplied password before it was hashed using the hashing algorithm defined by the preceding attribute values to generate the hashValue attribute, and which shall also be prepended to the user-supplied password before attempting to generate a hash value for comparison. A salt is a random string which is added to a user-supplied password before it is hashed in order to prevent a malicious party from pre-calculating all possible password/hash combinations and simply using those pre-calculated values (often referred to as a "dictionary attack").

If this attribute is omitted, then no salt shall be prepended to the user-supplied password before it is hashed for comparison with the stored hash value.

[Example: Consider an Office Open XML document with the following information stored in one of its protection elements:

<… saltValue="ZUdHa+D8F/OAKP3I7ssUnQ=="  hashValue="9oN7nWkCAyEZib1RomSJTjmPpCY=" />

The saltValue attribute value of ZUdHa+D8F/OAKP3I7ssUnQ== specifies that the user-supplied password must have this value prepended before it is run through the specified hashing algorithm to generate a resulting hash value for comparison. end example]

The possible values for this attribute are defined by the W3C XML Schema base64Binary datatype.

spinCount (Iterations to Run Hashing Algorithm)

Specifies the number of times the hashing function shall be iteratively run (runs using each iteration's result plus a 4 byte value (0-based, little endian) containing the number of the iteration as the input for the next iteration) when attempting to compare a user-supplied password with the value stored in the hashValue attribute.

[Rationale: Running the algorithm many times increases the cost of exhaustive search attacks correspondingly. Storing this value allows for the number of iterations to be increased over time to accommodate faster hardware (and hence the ability to run more iterations in less time). end rationale]

[Example: Consider an Office Open XML document with the following information stored in one of its protection elements:

<… spinCount="100000"  hashValue="9oN7nWkCAyEZib1RomSJTjmPpCY=" />

The spinCount attribute value of 100000 specifies that the hashing function must be run one hundred thousand times to generate a hash value for comparison with the hashValue attribute. end example]

The possible values for this attribute are defined by the ST_DecimalNumber simple type (§17.18.10).

[Note: The W3C XML Schema definition of this element’s content model (CT_WriteProtection) is located in §A.1. end note]

© ISO/IEC29500: 2008.

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

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