Explaining Fully Homomorphic Encryption to my Mom

tl;dr

• Traditional encryption = Baking bread by reading & following the recipe
• Homomorphic encryption = Baking bread without ever seeing the recipe

Traditional Encryption

1. Mom writes her secret bread recipe
2. She locks it (encrypts it)
3. She sends it to me (no one can steal it along the way)
4. I unlock it (decrypt) and read it
5. I follow the instructions and bake bread
6. I can share the unencrypted recipe with others

Note that both my mom and I have a version of the key. We can both lock or unlock the recipe. Afterwards, I could theoretically share the recipe with my friends who could bake bread themselves; though whether I should is another story 🙃.

Traditional Encryption Flow for a Secret Bread Recipe

Homomorphic Encryption

1. Mom writes her secret bread recipe
2. She locks it (encrypts it)
3. She sends it to me (no one can steal it along the way)
4. I do not unlock it
5. I magically follow the instructions and bake bread
6. I can share the encrypted recipe with others

Note that while my mom has a key she used to lock the recipe, I have a “magic key” that lets me follow the instructions without actually knowing what’s written inside. If I were to share the recipe with others, they’d need a version of the “magic key” as well.

Homomorphic Encryption Flow for a Secret Bread Recipe

Reality Check

Of course, there’s no literal “magic key.” Instead, it’s a mountain of math and cryptography. I don’t fully understand the details, but I do know that it’s slow and expensive.

Right now, homomorphic encryption works for small, simple online tasks. It’ll be a while before it’s fast and efficient enough to protect all of our online data.

And just for the record: I don’t actually bake bread. Here’s what usually happens instead…