Question regarding NVM writes for transient EC key updates

[kennychiu]

Hi NXP team,

Chip: OM-SE050 ARD-E Dev Kit

I have the following questions regarding EC key operations:

1. Create EC key
Se05x_API_WriteECKey(session_ctx, NULL, 0, 0x11223344, kSE05x_ECCurve_NIST_P256, NULL, 0, NULL, 0, kSE05x_INS_TRANSIENT, kSE05x_KeyPart_Pair);

2.Update EC key

Se05x_API_WriteECKey(session_ctx, NULL, 0, 0x11223344, kSE05x_ECCurve_NA, NULL, 0, NULL, 0, kSE05x_INS_TRANSIENT, kSE05x_KeyPart_Pair);

According to AN13483 section 8.1, For transient Secure Objects and for Crypto Objects, any update of the value of the Secure Object is not causing additional flash write operations

However, I noticed in SE-PLUG-TRUST-MW_04.07.00 simw-top/hostlib/hostLib/se05x_03_xx_xx/se05x_APDU_impl.h that Se05x_API_WriteECKey() contains the line: nLog("APDU", NX_LEVEL_WARN, "WriteECKey [] APDU causes NVM Writes");

Could you please clarify whether scenario 2 (updating a transient EC key with curveID = NA) will also cause NVM wear?

Thank you very much for your help.

[Kan_Li · Accepted solution]

Hi @kennychiu ,

Thanks for the reaching out! Yes, the statement in AN13483 section 8.1, For transient Secure Objects and for Crypto Objects, any update of the value of the Secure Object is not causing additional flash write operations is correct. so for scenario 2 (updating a transient EC key with curveID = NA) will not cause NVM wear. Please also note Creation and deletion of any Secure Object or Crypto Object is causing flash write operations, even you create an transient Secure Object.

Have a great day,
Kan

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