Chapter 2. API Reference
Calculate the HMAC hmac of a given message message with length message_len. SHA256 is used for
the calculation (fixed on ESP32S2).
Note Uses the HMAC peripheral in “upstream”mode.
Return
• ESP_OK, if the calculation was successful,
• ESP_FAIL, if the hmac calculation failed
Parameters
• key_id: Determines which of the 6 key blocks in the efuses should be used for the HMAC cal-
cuation. The corresponding purpose field of the key block in the efuse must be set to the HMAC
upstream purpose value.
• message: the message for which to calculate the HMAC
• message_len: message length return ESP_ERR_INVALID_STATE if unsuccessful
• [out] hmac: the hmac result; the buffer behind the provided pointer must be 32 bytes long
esp_err_t esp_hmac_jtag_enable(hmac_key_id_t key_id, const uint8_t *token)
Use HMAC peripheral in Downstream mode to re-enable the JTAG, if it is not permanently disable by HW.
In downstream mode HMAC calculations perfomred by peripheral used internally and not provided back to
user.
Return
• ESP_OK, if the calculation was successful, if the calculated HMAC value matches with provided
token, JTAG will be re-enable otherwise JTAG will remain disabled. Return value does not indicate
the JTAG status.
• ESP_FAIL, if the hmac calculation failed or JTAG is permanently disabled by
EFUSE_HARD_DIS_JTAG eFuse parameter.
• ESP_ERR_INVALID_ARG, invalid input arguments
Parameters
• key_id: Determines which of the 6 key blocks in the efuses should be used for the HMAC cal-
culation. The corresponding purpose field of the key block in the efuse must be set to HMAC
downstream purpose.
• token: Pre calculated HMAC value of the 32-byte 0x00 using SHA-256 and the known private
HMAC key. The key is already programmed to a eFuse key block. The key block number is provided
as the first parameter to this function.
esp_err_t esp_hmac_jtag_disable(void)
Disable the JTAG which might be enable using the HMAC downstream mode. This function just clear the
result generated by JTAG key by calling esp_hmac_jtag_enable() API.
Return
• ESP_OK return ESP_OK after writing the HMAC_SET_INVALIDATE_JTAG_REG with value
1.
Enumerations
enum hmac_key_id_t
The possible efuse keys for the HMAC peripheral
Values:
HMAC_KEY0 = 0
HMAC_KEY1
HMAC_KEY2
HMAC_KEY3
HMAC_KEY4
HMAC_KEY5
HMAC_KEY_MAX
Espressif Systems 275
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