Check a Change

Recompute Changed Tag

The changed inner hash flows into a changed outer tag.

highlighted = computed this step

The changed inner hash moves by one

The changed inner byte sum is 0x143, so the changed inner hash is 0x43.

changed inner=0x43\text{changed inner}=0x43
Recompute changed tagThe changed-message rows are recomputed from the same key and pads.Recompute changed tag - tag e7 changes to e8rowvaluecheckblock size2two-byte toy blockkey0f0epinned keyipad3636inner padinner key pad3938key xor ipadinner input39386869inner key pad || messageinner hash420x142 to 0x42opad5c5couter padouter key pad5352key xor opadouter input535242outer key pad || inner hashfinal tage70xe7 to 0xe7changed message686aone message byte changedchanged inner hash430x143 to 0x43changed final tage80xe8 to 0xe8old tag checkfaile7 != e8

The outer input uses the changed inner hash

The changed outer input is 0x535243.

changed outer input=0x535243\text{changed outer input}=0x535243
Recompute changed tagThe changed-message rows are recomputed from the same key and pads.Recompute changed tag - tag e7 changes to e8rowvaluecheckblock size2two-byte toy blockkey0f0epinned keyipad3636inner padinner key pad3938key xor ipadinner input39386869inner key pad || messageinner hash420x142 to 0x42opad5c5couter padouter key pad5352key xor opadouter input535242outer key pad || inner hashfinal tage70xe7 to 0xe7changed message686aone message byte changedchanged inner hash430x143 to 0x43changed final tage80xe8 to 0xe8old tag checkfaile7 != e8

The changed final tag is e8

The changed outer byte sum is 0xe8, so the changed final tag is 0xe8.

changed tag=0xe8\text{changed tag}=0xe8
Recompute changed tagThe changed-message rows are recomputed from the same key and pads.Recompute changed tag - tag e7 changes to e8rowvaluecheckblock size2two-byte toy blockkey0f0epinned keyipad3636inner padinner key pad3938key xor ipadinner input39386869inner key pad || messageinner hash420x142 to 0x42opad5c5couter padouter key pad5352key xor opadouter input535242outer key pad || inner hashfinal tage70xe7 to 0xe7changed message686aone message byte changedchanged inner hash430x143 to 0x43changed final tage80xe8 to 0xe8old tag checkfaile7 != e8

Summary

The recomputed tag for the changed message is 0xe8.

changed tag=0xe8\text{changed tag}=0xe8
Recompute changed tagThe changed-message rows are recomputed from the same key and pads.Recompute changed tag - tag e7 changes to e8rowvaluecheckblock size2two-byte toy blockkey0f0epinned keyipad3636inner padinner key pad3938key xor ipadinner input39386869inner key pad || messageinner hash420x142 to 0x42opad5c5couter padouter key pad5352key xor opadouter input535242outer key pad || inner hashfinal tage70xe7 to 0xe7changed message686aone message byte changedchanged inner hash430x143 to 0x43changed final tage80xe8 to 0xe8old tag checkfaile7 != e8