MAC
NIST message authentication codes
https://csrc.nist.gov/projects/message-authentication-codes
Glossary
NIST Glossary
https://csrc.nist.gov/glossary
message authentication code (MAC)
https://csrc.nist.gov/glossary/term/message_authentication_code
ChatGPT
How do you differentiate between NIST security MAC and Ethernet MAC?
Excellent question — they share the same acronym “MAC,” but refer to completely different concepts in different contexts.
Let’s clearly separate NIST security MAC and Ethernet MAC:
🧩 1. NIST Security MAC — Message Authentication Code
Domain: Cryptography / Information Security (NIST = National Institute of Standards and Technology)
Aspect Description
Full name Message Authentication Code
Purpose To verify data integrity and authenticity. Ensures the message was not altered and was created by someone with the shared secret key.
Defined by NIST (e.g., FIPS 198-1, SP 800-38B, etc.)
Mechanism Cryptographic function using a secret key and a message to produce a short tag (MAC).
Algorithms HMAC (Hash-based), CMAC (Block cipher-based), GMAC (Galois/Counter Mode-based)
Key property Depends on a shared secret key — only parties knowing the key can verify or create valid MACs.
Used in Secure protocols (TLS, IPsec, SSH), file integrity checking, firmware updates, etc.
Example HMAC-SHA256(message, key) → 32-byte tag
Analogy:
Think of it as a digital wax seal ensuring that a message has not been tampered with and came from the expected sender.
⚙️ 2. Ethernet MAC — Media Access Control Address
Domain: Networking / Data Link Layer (IEEE 802.3, OSI Layer 2)
Aspect Description
Full name Media Access Control (Address)
Purpose To uniquely identify a network interface card (NIC) on a local network.
Defined by IEEE (e.g., IEEE 802.3 for Ethernet)
Mechanism A 48-bit (or 64-bit) hardware address assigned to the NIC.
Format Usually written as AA:BB:CC:DD:EE:FF
Key property Used for frame delivery on the LAN; not secret, just an identifier.
Used in Ethernet, Wi-Fi, Bluetooth (Layer 2 communication)
Example 00:1A:2B:3C:4D:5E
Analogy:
Think of it as a postal address that uniquely identifies where to deliver network packets on a local network.
🧠 Summary Comparison
Feature NIST Security MAC Ethernet MAC
Full Form Message Authentication Code Media Access Control (Address)
Domain Cryptography / Security Networking / Data Link Layer
Standardization Body NIST (FIPS, SP) IEEE (802 family)
Function Data integrity + authenticity Device identification and frame routing
Secret Key Required Not used
Data Example Message → Tag Device → Address
Typical Algorithms HMAC, CMAC, GMAC N/A (fixed binary identifier)
Visibility Hidden (confidential) Public (visible in network traffic)
🔐 Rule of Thumb:
If you’re reading NIST/FIPS documents → MAC = Message Authentication Code (cryptographic).
If you’re dealing with Ethernet, Wi-Fi, or IEEE 802.x → MAC = Media Access Control (networking).
Would you like a diagram (e.g., PlantUML) showing how both types of MACs fit in their respective system stacks (cryptographic layer vs. OSI layer)?
Is there any other way to say the short name of the Message Authentication Code other than MAC?
Excellent follow-up — and yes, this is an important point because the acronym MAC is overloaded (especially confusing with Ethernet).
Let’s clarify:
🧩 1. Commonly accepted name
The formal short name is indeed “MAC”.
In NIST, ISO/IEC, and IETF documents, “MAC” almost always means Message Authentication Code when used in a cryptographic context.
Example:
NIST SP 800-38B — “Recommendation for Block Cipher Modes of Operation: The CMAC Mode for Authentication”
ISO/IEC 9797 — “Message Authentication Codes (MACs)”
⚠️ 2. Ambiguity problem
Because “MAC” also means “Media Access Control (address)” in networking, it can be confusing in mixed technical discussions (e.g., in embedded or automotive security where both appear).
✅ 3. Alternative ways to refer to it
Alternative Phrase Usage Context Comment
Auth tag or Authentication tag Cryptography (e.g., AES-GCM, ChaCha20-Poly1305) Common in modern AEAD (Authenticated Encryption with Associated Data) algorithms — equivalent in purpose to a MAC.
Integrity code or Integrity tag Generic / informal Used in documentation when avoiding acronym confusion.
Message tag Cryptographic libraries or specs Used in some APIs (e.g., OpenSSL, libsodium).
HMAC/CMAC/GMAC Specific algorithm Safest and clearest shorthand; e.g., “use HMAC-SHA256” rather than just “MAC.”
Authenticator Formal cryptographic term (NIST, ISO) Some documents use this instead of “MAC value.”
Code of authenticity (rare) Academic / explanatory Seen in older or educational materials, but not standard.
🧠 4. Recommended practice
Context Recommended Term Example
General cryptography “MAC (Message Authentication Code)” on first mention; “MAC” afterward “Compute the MAC using HMAC-SHA256.”
Mixed networking + security context Use “auth tag” or specific name like “HMAC” “The packet includes an HMAC-SHA256 for authentication.”
Documentation or teaching Expand once: “Message Authentication Code (MAC)” Prevents confusion with Ethernet MAC addresses.
🔍 5. Example of clear writing
“Each Ethernet frame carries a Media Access Control (MAC) address, while the payload includes a cryptographic HMAC-SHA256 tag — a Message Authentication Code ensuring integrity.”
Would you like me to show a table comparing “MAC,” “auth tag,” and “digital signature” — to clarify how they differ in authentication strength and use cases?
Is the phrase "message integrity code (MIC)" confusing?
That’s a very perceptive question — and yes, the term “Message Integrity Code (MIC)” is real and used in some standards, but it can be confusing depending on the audience and context.
Let’s unpack this carefully.
🧩 1. What “MIC” actually means
MIC = Message Integrity Code
It’s essentially the same functional idea as a MAC (Message Authentication Code) — a short cryptographic checksum that protects message integrity.
However:
MICs don’t always imply authenticity (shared secret authentication),
whereas MACs explicitly do.
So the subtle difference is:
🔒 MAC = Integrity + Authentication
🧾 MIC = Integrity (sometimes without authentication guarantee)
📚 2. Where “MIC” is actually used
Context Standard / Source Meaning
IEEE 802.11 (Wi-Fi) “Message Integrity Code (MIC)” field in WPA/TKIP frames Protects frames from tampering. Based on a keyed hash (so functionally a MAC, but called MIC).
Bluetooth Uses “MIC” in link-layer encryption Integrity check value appended to packets.
Zigbee / 802.15.4 Also defines “MIC” in the security header Integrity/authentication tag — same as a MAC.
IPsec / IETF RFCs Occasionally uses “Integrity Check Value (ICV)” instead of MIC Same functional purpose.
So:
✅ MIC is legitimate and standardized in several IEEE and wireless protocols.
❌ But outside those contexts, cryptographers almost universally use “MAC.”
⚠️ 3. Why “MIC” can be confusing
Source of confusion Explanation
Overlap with MAC People may not know whether “MIC” implies secret-key authentication or just a checksum.
Overlap with checksum/CRC Some engineers mistakenly equate “MIC” with simple error detection (like CRC), not cryptographic protection.
Terminology inconsistency NIST, ISO, and IETF don’t generally use “MIC.” IEEE does — so mixing them causes friction.
Abbreviation fatigue “MAC” (Media Access Control), “MIC” (Message Integrity Code), “ICV” (Integrity Check Value) all sound alike in security discussions.
✅ 4. Practical recommendation
Use Case Preferred Term Example
Cryptographic documentation / NIST / IETF MAC (HMAC, CMAC, GMAC) “Compute the MAC over the message using HMAC-SHA256.”
Wireless protocols (IEEE 802.11, Bluetooth, Zigbee) MIC “The WPA2 frame includes an 8-byte MIC field.”
Cross-domain documents (network + security) Be explicit “Compute an HMAC (message integrity code) over the payload.”
🧠 5. Quick summary
Term Expands to Typical Context Authentication Guarantee Common Standard
MAC Message Authentication Code NIST, IETF, cryptography ✅ Yes FIPS, SP 800
MIC Message Integrity Code IEEE 802.11, Bluetooth ✅ Usually (but not always clear) IEEE 802.11i
ICV Integrity Check Value IPsec, network protocols ✅ Yes RFC 4302
🔍 In short:
“MIC” is correct and standard in some IEEE protocols, but outside of those, it’s safer to say “MAC (Message Authentication Code)” or “auth tag.”
Would you like me to show a timeline of how the terms CRC → MIC → MAC → Auth Tag evolved across standards (IEEE, NIST, IETF)? It makes the historical reason for this naming clearer.
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＜この記事は個人の過去の経験に基づく個人の感想です。現在所属する組織、業務とは関係がありません。＞
This article is an individual impression based on my individual experience. It has nothing to do with the organization or business to which I currently belong.
Este artículo es una impresión personal basada en mi experiencia personal. No tiene nada que ver con la organización o empresa a la que pertenezco actualmente.
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