Patent Application
20060282683
The present invention relates to nonvolatile memory devices and more specifically to a mechanism to prevent unauthorized access to a nonvolatile memory device at the hardware level.
Flash memory and other non-volatile memory devices may be used to store secure, personal information, such as credit card data or other secret data. When secret data is stored on a flash memory device, it must remain secure. Today, much of the security provided for flash memory is performed in software or through a block lock feature. However, these methods may not be sufficient to prevent unauthorized malicious software from reading, programming, or erasing secret data stored in flash memory.
A better understanding of the present invention can be obtained from the following detailed description in conjunction with the following drawings, in which:
In the following description, for purposes of explanation, numerous details are set forth in order to provide a thorough understanding of embodiments of the present invention. However, it will be apparent to one skilled in the art that these specific details are not required in order to practice the present invention as hereinafter claimed.
Embodiments of the present invention concern secure non-volatile memory. Although the following discussion centers on flash memory, it will be understood by those skilled in the art that the present invention as hereinafter claimed may be practiced in support of any type of non-volatile memory.
A better understanding of the present invention can be obtained from the following detailed description in conjunction with the following drawings, in which:
One or more erase blocks 102 also include a secret region 104. The content of the secret region is visible only internally and may be modified or updated. Each block having a secret region may be individually secured at the hardware level. In one embodiment, all erase blocks include secret region 104. In one embodiment, the secret region is accessible only by logic or firmware within the flash memory, such as access control 108. Access control 108 may be implemented as a microcontroller within the flash device, or may be implemented as firmware.
The secret region 104 may be implemented as one or more additional wordlines within each erase block. The additional wordline(s) are not directly addressable by the user.
The secret region 104 is used to store a user configurable key. The key may be a 16-, 32-, 64- or X-bit number. When a key is stored in the secret region within a block, the key must be provided before the data in the block can be read, programmed, or erased.
The flash memory device 100 may be in a system which includes an external processing device 120. The processing device may be a microprocessor, a microcontroller, or another type of processing device. The processing device has access only to the control logic 106, but may not directly access the secret region 104.
Next, as illustrated in block 204, a command is issued to indicate that a key is to be programmed into the secret region within the block indicated by the block address. If the key is being programmed for the first time (block 206), a new key may be immediately issued (block 210). If the key has been previously programmed, the previous key must be issued (block 208) before a new key may be issued (block 210). This prevents the key from being overwritten by an unauthorized user.
The new key that is issued may be input directly by a user, or may be generated by a random number generator (RNG). Other algorithms or methods may be used to generate the new key as well. After the new key has been issued, a confirm command may be issued (block 212). The confirm command indicates that the issued new key is to be programmed in the secret region of the specified block.
Finally, as shown in block 214, the issued new key is programmed into the secret region of the addressed block. The programming of the key is an internal operation which occurs in the flash device after the confirm command is received.
After a key has been programmed in the secret region of a block, that block is secure, and may not be accessed unless the key is provided.
Next, as illustrated in block 304, a read array command is issued. After the read array command is issued, the key is issued (block 306). The programmed key is then read from the secret region of the secure block (block 308). The read of the secret region is done internally within the device itself, and cannot be performed based on a command from an external user. No one external to the device will be able to perform a read of the secret region.
The issued key is compared to the programmed key, as illustrated in block 310. In one embodiment, the issued key may be compared to the programmed key by embedded software in the flash device. In another embodiment, this comparison may be done by a hardware accelerator in the flash device.
If the issued key matches the programmed key, the read array command is allowed, and array data is output to the user (block 314). If the issued key does not match the programmed key, junk data is output (block 312).
In one embodiment, a counter may be used to determine how many times the issued key is compared to the programmed key before a match is made. If too many attempts are made before a match is made, and thus the counter exceeds a predetermined threshold value, the block may be retired. In such a manner, blocks could be rendered permanently inaccessible if an unauthorized user attempted to access a block.
Next, as illustrated in block 404, a program command is issued. After the program command is issued, the key is issued (block 406). The programmed key is then read from the secret region of the secure block (block 408).
As described above with respect to
Next, as illustrated in block 504, an erase command is issued. After the erase command is issued, the key is issued (block 506). The programmed key is then read from the secret region of the secure block (block 508).
As described above with respect to
Embodiments of the present invention may be used in any device requiring secure non-volatile memory storage. Examples of such devices include, but are not limited to handheld computing devices, mobile computing devices, and cellular telephones.
Thus, a method, apparatus, and system for flash array read, erase, and program security are disclosed. In the above description, numerous specific details are set forth. However, it is understood that embodiments may be practiced without these specific details. In other instances, well-known circuits, structures, and techniques have not been shown in detail in order not to obscure the understanding of this description. Embodiments have been described with reference to specific exemplary embodiments thereof. It will, however, be evident to persons having the benefit of this disclosure that various modifications and changes may be made to these embodiments without departing from the broader spirit and scope of the embodiments described herein. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.
