emSecure-ECDSA

Using emSecure-ECDSA

Using elliptic curves requires smaller key sizes for the same level of security. The keys use less memory when stored in an application, the algorithms run faster with smaller numbers, resulting in higher speeds. With a default key data can be signed in less than 160 ms.

All emSecure products are created to be simple but powerful, and easy to integrate. It can be used in new products and even extend existing ones as emSecure is a software solution and no additional hardware is required. The code is completely written in ANSI C and can be used platform- and controller-independent. The required key pairs can be generated with the included tool. The generated keys can be exported into different formats to be stored on the application code or loaded from a key file. This allows portability and exchangeability between different platforms. Signing data, for instance firmware images, can be done immediately with the included tool. It is also possible to integrate the signing process directly into a production application running on any PC or even on a microcontroller. Once a signature is generated, the signed data can be verified by its signature in an embedded application or on an external application communicating with the device. Verifying data typically takes less than 100 ms on a Cortex-M7, running at 216 MHz, which is not significantly more time for a bootloader to start a firmware.

Performance

emSecure-ECDSA aims for portability and is designed to fit speed and size requirements for different targets.
The process of verifying data is technically split up into two steps:

Step 1, the computation of the hash, depends on the size of the data, whereas step 2 is dependent on the key length and takes the same time to verify any data.

Step	Performance
SHA-256 Hash computation	3.70 MB/sec
ECDSA P-256 Signature verification	67.45 ms
ECDSA P-256 Signature generation	141.43 ms

Verifying Data: The following table shows some total values to verify different amounts of data.

Data size	Key curve	Signature verification	Hash computation	Total time
1 kByte	P-256	67.45 ms	0.27 ms	67.72 ms
100 kByte	P-256	67.45 ms	27.00 ms	94.45 ms

Signing Data: The following table shows some total values to sign different amounts of data.

Data size	Key curve	Signature generation	Hash computation	Total time
1 kByte	P-256	141.43 ms	0.27 ms	141.70 ms
100 kByte	P-256	141.43 ms	27.00 ms	168.43 ms

Test configuration:

Memory Footprint

	ROM	Static RAM	Stack P-256 key
Verification only:	9.2 KByte	0.04 KByte	2.4 KByte
Verification & Generation:	10.8 KByte	0.04 KByte	6.2 KByte

Test configuration:

Included Applications

emSecure includes all basic applications needed for securing a product. The applications’ source-code is included and provides an easy to use starting point for modifications and integration into other applications.

Application name	Target platform	Description
emKeyGen ECDSA	Windows	Generates a key pair with a given curve.
emSign ECDSA	Windows	Digitally signs a file with your private key.
emVerify ECDSA	Windows	Verifies the signature of a digital asset with its public key.
emPrintKey ECDSA	Windows	Exports keys and signatures into C source format, to be included into any application.

The sign and verify tools are available for evaluation.

The utilities are PC applications, ready-to-use for the setup step to secure your product.

Key generation:

emKeyGen ECDSA generates a public and a private key. The generation parameters can be set with command line options. The keys are saved in a common key file format and can be published and exchanged. Usage: emKeyGenECDSA.exe [<options>]</options>

Exporting keys:

emPrintKey exports key and signature files into a compileable format. The output can be linked into your application, so there is no need to load them from a file at runtime. This is especially useful for embedded applications.

Signing data:

emSign ECDSA digitally signs the file content, usually the data to be secured, with a given (private) key file and creates a signature file.

Verifying data:

emVerify ECDSA decrypts a signature file and verifies if the corresponding data file matches the signature.

Technical Background

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