How to use AES128 ECB for decryption

RE: How to use AES128 ECB for decryption

Guilherme de Paula — Fri, 24 Jan 2020 22:03:57 GMT

You are right! Sorry, I did this with an nRF51 in 2013 and had forgotten the details. The discussion you posted here has the correct solution. In the end you call the same function to encrypt/decrypt, but those extra steps are required.

RE: How to use AES128 ECB for decryption

WrightLin.Avnet — Wed, 01 Jan 2020 16:29:44 GMT

I think it is not quite right that you could get the decrypt message just by change the location of cleartext and ciphertext.

It was discussed in this thread:
https://devzone.nordicsemi.com/f/nordic-q-a/6308/how-to-decrypt-aes-ecb-nopadding-data#comment-40082

AES is symmetric (block) cipher which means that there is 1 shared key which is used for both encryption (ENC) and decryption (DEC).
But ENC and DEC functions are inverse and in general these are mathematical completely different when it comes to actual computation. So NO, you cannot use the same function for going there and back unless it implements both encrypt and decrypt mode (e.g. with some flag in the call).

And the proper way to do encrypt and decrypt is described detailly in here:
https://devzone.nordicsemi.com/nordic/nordic-blog/b/blog/posts/intro-to-application-level-security-using-the-ecb-

Wright

RE: How to use AES128 ECB for decryption

Guilherme de Paula — Thu, 16 May 2019 01:56:31 GMT

The key in .key, and the input data in .cleartext, then call the function, then the output data will be in .ciphertext

You call the same function sd_ecb_block_encrypt whether you want to encrypt or decrypt. The operation is symmetrical.

RE: How to use AES128 ECB for decryption

Guilherme de Paula — Thu, 16 May 2019 01:54:01 GMT

You put your encryption/decryption key in .key, and the data to be encrypted/decrypted in .cleartext (think of it as "input") ... then you call sd_ecb_block_encrypt and it will have the result in .ciphertext (think of it as "output").

You do the same thing whether you want to encrypt or decrypt. The operation is symetrical.

RE: How to use AES128 ECB for decryption

JW de Wit — Tue, 15 Jul 2014 13:32:56 GMT

I was looking for the same, seems like the hardware only has enryption and no decryption. In ble connections this is sufficient while the counter mode is used. In countermode messages are both enrcypted and decripted using AES (ECB)encryption of a counter value, so ECB decription not needed for bluetooth and it seems Nordic made the hardware to fit BLE security and just BLE security .

RE: How to use AES128 ECB for decryption

Ivan Gómez — Tue, 15 Jul 2014 09:53:04 GMT

I am only able to post once so... I edit this one.

Now I get no errors and warnings building my code but once I try to use AES in order to upload the app code to the nRF51822 BLUETOOTH SMART BEACON KIT, it stop working... The code I used is the following:

nrf_ecb_hal_data_t *aestructura;

	*(*aestructura).key=0x12;
	*(*aestructura).cleartext=16;
//Aplicacion de AES
sd_ecb_block_encrypt(aestructura);
	encriptado=*(*aestructura).ciphertext;
	printf("Encrypted TEXT: %d",encriptado);

Regards,

Iván

I am trying to encypt some data too. I think the first one is the right way in order to encrypt because you have the struct nrf_ecb_hal_data_t which defines the 3 parameters needed for the encryptation. Anyway I don't know what to put in those parameters:

nrf_ecb_hal_data_t aestructura; aestructura.key=12345678; aestructura.cleartext="what should I put here"; aestructura.ciphertext="what should I put here";

After that I suppose we only should use the function: sd_ecb_block_encrypt(aestructura));

And it should give back the encrypted data? Don't know yet.

I hope some of this can help you a bit, I have many questions though.

Regards

Iván