aescmac

pki/aescmac

Import path: github.com/InsideGallery/core/pki/aescmac

aescmac implements AES-CMAC and small byte helpers used by key diversification code. It returns standard hash.Hash values for incremental MAC calculation and also provides a one-shot Sum helper.

Main API

• NewCMAC(key) returns a hash.Hash for AES-CMAC. Keys must be 16, 24, or 32 bytes.
• Sum(key, data) computes a one-shot AES-CMAC value.
• ErrUnsupportedKeySize reports unsupported key sizes.
• Xor(a, b) returns the byte-wise XOR of equal-length slices and returns nil on length mismatch.
• ShiftLeft(data) shifts a byte slice left by one bit with carry propagation.
• Padding(data) appends the CMAC padding marker and zero padding as needed.
• ErrAlreadyFinished and ErrXorLengthMismatch are exported for compatibility; the current hash.Hash usage does not normally surface them from Sum.

Usage

package example

import "github.com/InsideGallery/core/pki/aescmac"

func mac(data []byte) ([]byte, error) {
	key := make([]byte, 16)

	return aescmac.Sum(key, data)
}

For incremental input:

h, err := aescmac.NewCMAC(key)
if err != nil {
	return nil, err
}
if _, err := h.Write(part1); err != nil {
	return nil, err
}
if _, err := h.Write(part2); err != nil {
	return nil, err
}
tag := h.Sum(nil)

Security Notes

The implementation is validated by tests against RFC 4493 vectors. Compare MAC tags with a constant-time comparison, and keep CMAC keys in secret storage.