Microsoft Office password protection

Last updated

Microsoft Office password protection is a security feature that allows Microsoft Office documents (e.g. Word, Excel, PowerPoint) to be protected with a user-provided password.

Contents

Types

There are two types of passwords that can be set to a document: [1]

History of Office encryption

Weak encryptions

In Excel and Word 95 and prior editions a weak protection algorithm is used that converts a password to a 16-bit verifier and a 16-byte XOR obfuscation array [1] key. [4] Hacking software is now readily available to find a 16-byte key and decrypt the password-protected document. [5]

Office 97, 2000, XP and 2003 use RC4 with 40 bits. [4] The implementation contains multiple vulnerabilities rendering it insecure. [5]

In Office XP and 2003 an opportunity to use a custom protection algorithm was added. [4] Choosing a non-standard Cryptographic Service Provider allows increasing the key length. Weak passwords can still be recovered quickly even if a custom CSP is on.

AES since Office 2007

In Office 2007, protection was significantly enhanced since a modern protection algorithm named Advanced Encryption Standard was used. [4] At present[ when? ], there is no software that can break this encryption. With the help of the SHA-1 hash function, the password is stretched into a 128-bit key 50,000 times before opening the document; as a result, the time required to crack it is vastly increased, similar to PBKDF2, scrypt or other KDFs.[ citation needed ]

Office 2010 employed AES and a 128-bit key, but the number of SHA-1 conversions doubled to 100,000. [4]

Office 2013 uses 128-bit AES, again with hash algorithm SHA-1 by default. [6] It introduces SHA-512 hashes in the encryption algorithm, making brute-force and rainbow table attacks slower.[ citation needed ]

Office 2016 uses, by default, 256-bit AES, the SHA-2 hash algorithm, 16 bytes of salt and CBC (cipher block chaining). [7]

Attacks that target the password include dictionary attacks, rule-based attacks, brute-force attacks, mask attacks and statistics-based attacks. Attacks can be sped up through multiple CPUs, also in the cloud, and GPGPU (applicable only to Office 2007-10 documents).[ citation needed ]

Excel worksheets and macro protection

The protection for worksheets and macros is necessarily weaker than that for the entire workbook, as the software itself must be able to display or use them.[ citation needed ]

For XLSX files that can be opened but not edited, there is another attack. As the file format is a group of XML files within a ZIP; unzipping, editing, and replacing the workbook.xml file (and/or the individual worksheet XML files) with identical copies in which the unknown key and salt are replaced with a known pair or removed altogether allows the sheets to be edited.[ citation needed ]

Related Research Articles

Blowfish is a symmetric-key block cipher, designed in 1993 by Bruce Schneier and included in many cipher suites and encryption products. Blowfish provides a good encryption rate in software, and no effective cryptanalysis of it has been found to date. However, the Advanced Encryption Standard (AES) now receives more attention, and Schneier recommends Twofish for modern applications.

<span class="mw-page-title-main">Microsoft Excel</span> Spreadsheet editor, part of Microsoft 365

Microsoft Excel is a spreadsheet editor developed by Microsoft for Windows, macOS, Android, iOS and iPadOS. It features calculation or computation capabilities, graphing tools, pivot tables, and a macro programming language called Visual Basic for Applications (VBA). Excel forms part of the Microsoft 365 suite of software.

In cryptography, RC4 is a stream cipher. While it is remarkable for its simplicity and speed in software, multiple vulnerabilities have been discovered in RC4, rendering it insecure. It is especially vulnerable when the beginning of the output keystream is not discarded, or when nonrandom or related keys are used. Particularly problematic uses of RC4 have led to very insecure protocols such as WEP.

<span class="mw-page-title-main">Symmetric-key algorithm</span> Algorithm

Symmetric-key algorithms are algorithms for cryptography that use the same cryptographic keys for both the encryption of plaintext and the decryption of ciphertext. The keys may be identical, or there may be a simple transformation to go between the two keys. The keys, in practice, represent a shared secret between two or more parties that can be used to maintain a private information link. The requirement that both parties have access to the secret key is one of the main drawbacks of symmetric-key encryption, in comparison to public-key encryption. However, symmetric-key encryption algorithms are usually better for bulk encryption. With exception of the one-time pad they have a smaller key size, which means less storage space and faster transmission. Due to this, asymmetric-key encryption is often used to exchange the secret key for symmetric-key encryption.

Transport Layer Security (TLS) is a cryptographic protocol designed to provide communications security over a computer network. The protocol is widely used in applications such as email, instant messaging, and voice over IP, but its use in securing HTTPS remains the most publicly visible.

<span class="mw-page-title-main">Cryptographic hash function</span> Hash function that is suitable for use in cryptography

A cryptographic hash function (CHF) is a hash algorithm that has special properties desirable for a cryptographic application:

<span class="mw-page-title-main">MD4</span> Cryptographic hash function

The MD4 Message-Digest Algorithm is a cryptographic hash function developed by Ronald Rivest in 1990. The digest length is 128 bits. The algorithm has influenced later designs, such as the MD5, SHA-1 and RIPEMD algorithms. The initialism "MD" stands for "Message Digest".

The Encrypting File System (EFS) on Microsoft Windows is a feature introduced in version 3.0 of NTFS that provides filesystem-level encryption. The technology enables files to be transparently encrypted to protect confidential data from attackers with physical access to the computer.

NSA Suite B Cryptography was a set of cryptographic algorithms promulgated by the National Security Agency as part of its Cryptographic Modernization Program. It was to serve as an interoperable cryptographic base for both unclassified information and most classified information.

ECRYPT was a 4-year European research initiative launched on 1 February 2004 with the stated objective of promoting the collaboration of European researchers in information security, and especially in cryptology and digital watermarking.

Strong cryptography or cryptographically strong are general terms used to designate the cryptographic algorithms that, when used correctly, provide a very high level of protection against any eavesdropper, including the government agencies. There is no precise definition of the boundary line between the strong cryptography and (breakable) weak cryptography, as this border constantly shifts due to improvements in hardware and cryptanalysis techniques. These improvements eventually place the capabilities once available only to the NSA within the reach of a skilled individual, so in practice there are only two levels of cryptographic security, "cryptography that will stop your kid sister from reading your files, and cryptography that will stop major governments from reading your files".

In a Windows network, NT LAN Manager (NTLM) is a suite of Microsoft security protocols intended to provide authentication, integrity, and confidentiality to users. NTLM is the successor to the authentication protocol in Microsoft LAN Manager (LANMAN), an older Microsoft product. The NTLM protocol suite is implemented in a Security Support Provider, which combines the LAN Manager authentication protocol, NTLMv1, NTLMv2 and NTLM2 Session protocols in a single package. Whether these protocols are used or can be used on a system which is governed by Group Policy settings, for which different versions of Windows have different default settings.

In cryptography, key stretching techniques are used to make a possibly weak key, typically a password or passphrase, more secure against a brute-force attack by increasing the resources it takes to test each possible key. Passwords or passphrases created by humans are often short or predictable enough to allow password cracking, and key stretching is intended to make such attacks more difficult by complicating a basic step of trying a single password candidate. Key stretching also improves security in some real-world applications where the key length has been constrained, by mimicking a longer key length from the perspective of a brute-force attacker.

Institute of Electrical and Electronics Engineers (IEEE) standardization project for encryption of stored data, but more generically refers to the Security in Storage Working Group (SISWG), which includes a family of standards for protection of stored data and for the corresponding cryptographic key management.

<span class="mw-page-title-main">Private Disk</span>

Private Disk is a disk encryption application for the Microsoft Windows operating system, developed by Dekart SRL. It works by creating a virtual drive, the contents of which is encrypted on-the-fly; other software can use the drive as if it were a usual one.

<span class="mw-page-title-main">Cryptography</span> Practice and study of secure communication techniques

Cryptography, or cryptology, is the practice and study of techniques for secure communication in the presence of adversarial behavior. More generally, cryptography is about constructing and analyzing protocols that prevent third parties or the public from reading private messages. Modern cryptography exists at the intersection of the disciplines of mathematics, computer science, information security, electrical engineering, digital signal processing, physics, and others. Core concepts related to information security are also central to cryptography. Practical applications of cryptography include electronic commerce, chip-based payment cards, digital currencies, computer passwords, and military communications.

The following outline is provided as an overview of and topical guide to cryptography:

There are various implementations of the Advanced Encryption Standard, also known as Rijndael.

crypt is a POSIX C library function. It is typically used to compute the hash of user account passwords. The function outputs a text string which also encodes the salt, and identifies the hash algorithm used. This output string forms a password record, which is usually stored in a text file.

This is a list of cybersecurity information technology. Cybersecurity is security as it is applied to information technology. This includes all technology that stores, manipulates, or moves data, such as computers, data networks, and all devices connected to or included in networks, such as routers and switches. All information technology devices and facilities need to be secured against intrusion, unauthorized use, and vandalism. Additionally, the users of information technology should be protected from theft of assets, extortion, identity theft, loss of privacy and confidentiality of personal information, malicious mischief, damage to equipment, business process compromise, and the general activity of cybercriminals. The public should be protected against acts of cyberterrorism, such as the compromise or loss of the electric power grid.

References

  1. 1 2 "[MS-OFFCRYPTO] Office Document Cryptography Structure" (PDF). Microsoft Corporation. 2021-10-05. pp. 60–65. Archived (PDF) from the original on 2023-04-11.
  2. ↑ "How to Open a Password-Protected Excel File". wikihow.com. Retrieved 2024-01-24.
  3. ↑ "Password protect documents, workbooks, and presentations". Office.microsoft.com. Retrieved 26 December 2012.
  4. 1 2 3 4 5 "Microsoft Office File Format Documents". Msdn.microsoft.com. Retrieved 26 December 2012.
  5. 1 2 Wu, Hongjun (2005). "The Misuse of RC4 in Microsoft Word and Excel" (PDF). Institute for Infocomm Research, Singapore.
  6. ↑ "Cryptography and encryption settings for Office 2013". docs.microsoft.com. 26 December 2016. Retrieved 4 July 2018.
  7. ↑ DHB-MSFT. "Cryptography and encryption in Office 2016". docs.microsoft.com. Retrieved 2018-12-07.


This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.