ESP32 Forum

Posted: **Tue Oct 07, 2025 2:00 pm**

I have been doing a basic test of soft locking and unlocking the JTAG. My SDK = v5.5.0

I have a test key

const uint8_t keyData[32] = 
{
    0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08,
    0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, 0x0F, 0x10,
    0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18,
    0x19, 0x1A, 0x1B, 0x1C, 0x1D, 0x1E, 0x1F, 0x20
};

which is written using

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esp_efuse_write_key( EFUSE_BLK_KEY3, ESP_EFUSE_KEY_PURPOSE_HMAC_DOWN_JTAG, keyData, sizeof(keyData) );

This appears to work as it has returned ESP_OK

I don't need to perform the hmac calculation (keeping things simple) as I know that after the calculation on a 32 byte zero message, it will be

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const uint8_t zerosHmac[32] =
{
    0xb2, 0xa4, 0x9b, 0x1c, 0xce, 0x1b, 0xe9, 0x22, 
    0xbb, 0x7e, 0x43, 0x12, 0x77, 0x41, 0x3e, 0x3e, 
    0x8e, 0x6c, 0x3e, 0x8e, 0x6e, 0x17, 0x62, 0x5c, 
    0x50, 0xac, 0x66, 0xa9, 0xa8, 0x57, 0x94, 0x9b
};

At this point I have confirmed that my device is soft locked by using espefuse to read out the summary and confirming that openocd can't connect. Originaly it could.

I then attempt to soft unlock using

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esp_hmac_jtag_enable(HMAC_KEY3, zerosHmac);

It returns EST_FAIL as ets_jtag_enable_temporarily(), that is within esp_hmac_jtag_enable(), has failed.

ESP32 Forum

ESP32-C5 soft locked JTAG but can't soft unlock.

ESP32-C5 soft locked JTAG but can't soft unlock.