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How does AES GCM encryption work

• Previously utilized AES CBC 256 encryption with a 256-bit key and 128-bit IV, but experienced performance issues.
• Transitioned to AES GCM encryption using a 256-bit key and 96-bit IV to enhance performance.
• The authentication tag is crucial for both AES GCM encryption and decryption; it can be prepended to the ciphertext for convenient access during decryption.
• There are concerns regarding the necessity of hiding the auth tag from attackers; it is generally not considered sensitive like the ciphertext.
• Reusing an IV can result in repeated patterns in encrypted ciphertexts, even with different messages, due to identical letters.
• Reusing an IV in CBC mode poses risks, but in GCM mode, it can be catastrophic, particularly if the same IV is used for multiple messages from a single sender.
• "AuthenticatedData" in AES GCM refers to additional data that is authenticated but not encrypted, ensuring the integrity and authenticity of the data.
• For further details on AuthenticatedData in AES GCM, consult the Apple Developer documentation.

The Ultimate Developer's Guide to AES-GCM: Encrypt and ...

• The guide details the use of the Web Cryptography API for secure data protection via AES-GCM encryption, focusing on key management, encryption processes, and integrity checks.

• AES-GCM (Advanced Encryption Standard — Galois/Counter Mode) is a symmetric key encryption algorithm that uses the same key for both encryption and decryption, enhancing security through PBKDF2 for key derivation.

• PBKDF2 (Password-Based Key Derivation Function 2) converts user passwords into strong cryptographic keys, using a salt to thwart rainbow table attacks and multiple iterations to resist brute-force attacks.

• Key derivation involves a user password, a random salt, and PBKDF2 to create a secure encryption key that is much harder to guess than the original password.

• The encryption process generates a unique Initialization Vector (IV) for each operation, encrypts plaintext data with the derived key, and produces ciphertext along with an authentication tag for integrity verification.

• A 12-byte IV is optimal for AES-GCM, aligning with AES's block size, enhancing security, and complying with NIST recommendations, allowing for numerous encryptions with the same key.

• The decryption process reverses encryption steps, requiring the same key, IV, and authentication tag to retrieve the original plaintext while ensuring data integrity.

• A complete code example illustrates the AES-GCM encryption and decryption process using the Web Cryptography API, including functions for key derivation, data encryption, and decryption.

• Best practices for storing and transmitting encrypted data include keeping ciphertext, IV, and salt public, as they do not need to be secret; only the encryption key must be protected.

• Salt, like the Initialization Vector (IV), can be publicly stored or transmitted and is essential for deriving the same encryption key during decryption.

• The Authentication Tag is vital for verifying the integr…

AES-GCM authenticated encryption

• AES-GCM (Galois/Counter Mode) provides authenticated encryption, ensuring confidentiality and authentication, while enabling integrity checks for additional authenticated data (AAD) sent in clear text.
• The specifications for AES-GCM are outlined in NIST Special Publication 800-38D.
• Four inputs are necessary for authenticated encryption: a secret key, an initialization vector (IV or nonce), plaintext, and optional AAD, with the nonce and AAD transmitted in clear text.
• The encryption process produces two outputs: ciphertext (which is the same length as the plaintext) and an authentication tag (also known as a message authentication code or integrity check value).
• This Toolkit implements AES-GCM in accordance with RFC 5116, which defines the interface and algorithms for authenticated encryption.
• The Toolkit mandates a fixed-length nonce (IV) of 12 bytes (96 bits) and a fixed-length tag of 16 bytes (128 bits), with no options for varying these lengths.
• Support is provided for the AES-192-GCM algorithm, in addition to AES-128-GCM and AES-256-GCM as specified in RFC 5116.
• The authentication tag is automatically appended to the encryption output, and the IV can optionally be prepended, following the guidelines from XML Encryption Syntax and Processing Version 1.1.
• In this context, the terms "IV" and "nonce" are used interchangeably.

aes - What is the use of Additional data or associated ...

• The algorithms are designed to detect tampering with encrypted data, ensuring the receiver receives the intended message from the sender.

• An authentication tag, derived from the ciphertext, verifies message integrity; any modification by an attacker will likely result in a mismatched tag, causing message rejection.

• Additional Authenticated Data (AAD) mitigates the risk of replay attacks, where an attacker could resend a message in a different context to mislead the recipient.

• AAD allows the sender to define the message context during encryption, ensuring that the receiver can only decrypt messages meant for that specific context.

• If the AAD used during encryption does not match the expected AAD by the receiver, the tags will not align, leading to message rejection.

• AAD can consist of any identifying string, such as a serial number or a question related to a response, providing context for the encrypted message.

• In cases where only a single message is encrypted with a key, AAD can be omitted, as its additional security may not be necessary.

• The authentication process's effectiveness depends on assumptions, including that the attacker does not know the AES key, that AES is secure, and that the attacker has not observed two valid ciphertexts with the same nonce.

GCM Mode

• Galois/Counter Mode (GCM) is a block cipher mode that employs the Advanced Encryption Standard (AES) algorithm, supporting key lengths of 128, 192, or 256 bits.
• GCM processes data in fixed-sized blocks of 128 bits and requires the lengths of both the payload and additional authenticated data (AAD) to be specified in bits.
• The implementation of GCM on FPGA supports both encryption and decryption, with specific bit-widths for parameters detailed in a table.
• The initialization vector (IV) must be exactly 96 bits to ensure compatibility and efficiency, following standard guidelines.
• During decryption, a Message Authentication Code (MAC) is used instead of a failure flag, and matching MACs from both encryption and decryption confirm data authenticity.
• The GCM encryption process involves two components: Counter Mode (CTR) for converting plaintext to ciphertext and Galois Message Authentication Code (GMAC) for generating the MAC.
• The decryption process is similar to encryption, primarily differing in the conversion of ciphertext back to plaintext.
• The encryption module consists of two parallel components: aesGctrEncrypt and genGMAC, which communicate through data streams to optimize resource usage.
• Profiling data for GCM-AES128, GCM-AES192, and GCM-AES256 includes resource utilization metrics (CLB, LUT, FF, etc.) and critical path timing for both encryption and decryption.
• GCM-AES128 encryption requires 3836 CLBs with a critical path of 3.165 ns, while decryption needs 3711 CLBs and has a critical path of 2.885 ns.
• GCM-AES192 encryption utilizes 4324 CLBs with a critical path of 2.854 ns, and decryption requires 4504 CLBs with a critical path of 2.899 ns.
• GCM-AES256 encryption demands 4777 CLBs and has a critical path of 2.955 ns, while decryption requires 5130 CLBs with a critical path of 3.077 ns.