ModificationVerifier Class
Modification Verifier.When the object is serialized out as xml, its qualified name is p:modifyVerifier.
Inheritance Hierarchy
System.Object
DocumentFormat.OpenXml.OpenXmlElement
DocumentFormat.OpenXml.OpenXmlLeafElement
DocumentFormat.OpenXml.Presentation.ModificationVerifier
Namespace: DocumentFormat.OpenXml.Presentation
Assembly: DocumentFormat.OpenXml (in DocumentFormat.OpenXml.dll)
Syntax
'Declaration
Public Class ModificationVerifier _
Inherits OpenXmlLeafElement
'Usage
Dim instance As ModificationVerifier
public class ModificationVerifier : OpenXmlLeafElement
Remarks
[ISO/IEC 29500-1 1st Edition]
19.2.1.19 modifyVerifier (Modification Verifier)
This element specifies the write protection settings which have been applied to a PresentationML document. Write protection refers to a mode in which the document's contents should not be modified, and the document should not be resaved using the same file name.
When present, the application shall require a password to enable modifications to the document. If the supplied password does not match the hash value in this attribute, then write protection shall be enabled. If this element is omitted, then no write protection shall be applied to the current document. Since this protection does not encrypt the document, malicious applications might circumvent its use.
The password supplied to the algorithm is to be a UTF-16LE encoded string; strings longer than 255 characters are truncated to 255 characters. If there is a leading BOM character (U+FEFF) in the encoded password it is removed before hash calculation. The attributes of this element specify the algorithm to be used to verify the password provided by the user.
[Example: Consider a PresentationML document that can only be opened 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 PresentationML:
<p:modifyVerifier p:algorithmName="SHA-512" … p:hashValue="9oN7nWkCAyEZib1RomSJTjmPpCY=" … />
…In order for the hosting application to enable edits to the document, the hosting application would have to be provided with a password that the hosting application would then hash using the algorithm specified by the algorithm attributes and compare to the value of the hashValue attribute (9oN7nWkCAyEZib1RomSJTjmPpCY=). If the two values matched, the file would be opened in an editable state. end example]
Parent Elements |
|---|
presentation (§19.2.1.26) |
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 ISO/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 ISO/IEC 10118-3:2004 shall be used. SHA-1 Specifies that the SHA-1 algorithm, as defined by ISO/IEC 10118-3:2004 shall be used. SHA-256 Specifies that the SHA-256 algorithm, as defined by ISO/IEC 10118-3:2004 shall be used. SHA-384 Specifies that the SHA-384 algorithm, as defined by ISO/IEC 10118-3:2004 shall be used. SHA-512 Specifies that the SHA-512 algorithm, as defined by ISO/IEC 10118-3:2004 shall be used. WHIRLPOOL Specifies that the WHIRLPOOL algorithm, as defined by ISO/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 W3C XML Schema string datatype. |
hashValue (Password Hash Value) |
Specifies the hash value for the password required to edit this chartsheet. 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. |
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. |
spinValue (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. |
[Note: The W3C XML Schema definition of this element’s content model (CT_ModifyVerifier) is located in §A.3. end note]
© ISO/IEC29500: 2008.
Thread Safety
Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.