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FileSharing class

Defines the FileSharing Class. When the object is serialized out as xml, its qualified name is x:fileSharing.

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

public class FileSharing : OpenXmlLeafElement

[ISO/IEC 29500-1 1st Edition]

fileSharing (File Sharing)

This element tracks file sharing settings for the workbook. When a password is to be hashed and stored in this element, it shall be hashed starting from a UTF-16LE encoded string value. If there is a leading BOM character (U+FEFF) in the encoded password it is removed before hash calculation.

Parent Elements

workbook (§18.2.27)

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_Xstring simple type (§22.9.2.19).

hashValue (Password Hash Value)

Specifies the hash value for the password required for editing this workbook. 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 cryptAlgorithmSid attribute value of 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.

readOnlyRecommended (Read Only Recommended)

Specifies a boolean value that indicates on open, whether the application alerts the user that the file be marked as read-only.

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

saltValue (Salt Value for Password Verifier)

Specifies the salt that 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 that 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 W3C XML Schema unsignedInt datatype.

userName (User Name)

Specifies the username of the person with write reservation for this workbook.

The possible values for this attribute are defined by the ST_Xstring simple type (§22.9.2.19).

[Note: The W3C XML Schema definition of this element’s content model (CT_FileSharing) is located in §A.2. 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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