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Patrick
Patrick
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I have messages with the following fixed lengths:

  • 4 byte
  • 8 byte
  • 16 byte

I want to encrypted them and prevent modification by appending an authentication tag using a MAC algorithm of my choosing (e.g. using Encrypt-then-Mac schema). Additionally I want the cipher output message to be as short as possible.

Let's say the normal MAC output size would be 16 byte (e.g CMAC with AES). Can I truncate the MAC with a short message like 4 byte to get similar security assurances?

According to various NIST standards, minimum lengths of MAC from 64 bit (CMAC) to 96 bit (GMAC) are recommended.

I have messages with the following fixed lengths:

  • 4 byte
  • 8 byte
  • 16 byte

I want to encrypted them and prevent modification by appending an authentication tag using a MAC algorithm of my choosing (e.g. using Encrypt-then-Mac schema). Additionally I want the cipher output message to be as short as possible.

Let's say the normal MAC output size would be 16 byte (e.g CMAC with AES). Can I truncate the MAC with a short message like 4 byte to get similar security assurances?

I have messages with the following fixed lengths:

  • 4 byte
  • 8 byte
  • 16 byte

I want to encrypted them and prevent modification by appending an authentication tag using a MAC algorithm of my choosing (e.g. using Encrypt-then-Mac schema). Additionally I want the cipher output message to be as short as possible.

Let's say the normal MAC output size would be 16 byte (e.g CMAC with AES). Can I truncate the MAC with a short message like 4 byte to get similar security assurances?

According to various NIST standards, minimum lengths of MAC from 64 bit (CMAC) to 96 bit (GMAC) are recommended.

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Patrick
Patrick
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  • 27

What Are Secure Limits to Truncate the Authentication Tag (Mac) for Short Messages?

I have messages with the following fixed lengths:

  • 4 byte
  • 8 byte
  • 16 byte

I want to encrypted them and prevent modification by appending an authentication tag using a MAC algorithm of my choosing (e.g. using Encrypt-then-Mac schema). Additionally I want the cipher output message to be as short as possible.

Let's say the normal MAC output size would be 16 byte (e.g CMAC with AES). Can I truncate the MAC with a short message like 4 byte to get similar security assurances?