# External flash
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External 256kbytes flash is a unique feature of the RDV4 edition.

# Table of Contents
- [External flash](#external-flash)
- [Table of Contents](#table-of-contents)
  - [Addresses](#addresses)
  - [Layout](#layout)
  - [Page3 Layout](#page3-layout)
  - [RSA signature](#rsa-signature)
- [backup first!](#backup-first)



## Addresses
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Flash memory is

* 256KB (0x40000 = 262144)
* divided into 4 pages of 64KB (0x10000 = 65536)
* 4 pages divided into 16 sectors of 4KB (0x1000 = 4096), so last sector is at 0x3F000

Therefore a flash address can be interpreted as such:
```
0xPSxxx       e.g. 0x3FF7F
  ^ page             ^ page 3
   ^ sector           ^ sector 0xF
    ^^^ offset         ^^^ offset 0xF7F
```

Please note that for other flash memory sizes than 256KB a "Page 3" will be the last page of the memory, and address offsets would be dependant on the memory size.

## Layout
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Page 0:
* available for user data
* to dump it: `mem dump -f page0_dump -o 0 -l 65536`
* to erase it: `mem wipe -p 0`

Page 1:
* available for user data
* to dump it: `mem dump -f page1_dump -o 65536 -l 65536`
* to erase it: `mem wipe -p 1`

Page 2:
* available for user data
* to dump it: `mem dump -f page2_dump -o 131072 -l 65536`
* to erase it: `mem wipe -p 2`

Page 3 (or the last page for memories other than 256KB):
* used by Proxmark3 RDV4 specific functions: flash signature, see below for details
* to dump it: `mem dump -f page3_dump -o 196608 -l 65536`
* to erase it:
  * **Beware** it will erase your flash signature so better to back it up first as you won't be able to regenerate it by yourself!
  * edit the source code to enable Page 3 as a valid input in the `mem wipe` command.
  * Updating keys dictionaries doesn't require to erase page 3.

## Page3 Layout
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Page3 (or the last page for memories other than 256KB) is used as follows by the Proxmark3 RDV4 firmware:

* **RSA SIGNATURE**, see below for details
  * offset: page 3 sector 15 (0xF) offset 0xF7F @ 3*0x10000+15*0x1000+0xF7F=0x3FF7F  (decimal 262015)
  * length: 128 bytes
  * offset should have been 0x3FF80 but historically it's one byte off and therefore the last byte of the flash is unused

* **Reserved for future use**
  * offset: page 3 sector 14 (0xE)

* **SPIFFS sectors**
  * offset: page 3 sectors 13..0 (0xD..0x0)

## RSA signature
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To ensure your Proxmark3 RDV4 is not a counterfeit product, its external flash contains a RSA signature of the flash unique ID.
You can verify it with: `mem info`


Here below is a sample output of a RDV4 device.
```
[usb] pm3 --> mem info                                                
                                                                      
[=] --- Flash memory Information ---------                            
[=] ID................... 25AD99A782A867D5                            
[=] SHA1................. 67C3B9BA2FA90AD4B283926B70017066C082C156    
[+] Signature............ ( ok )                                      
                                                                      
[=] --- RDV4 RSA signature ---------------                            
[=]  C7C7DF7FA3A2391A2B36E97D227C746ED8BB475E8766F54A13BAA9AAB29299BE 
[=]  37546AACCC29157ABF8AFBF3A1CFB24275442D565F7E996C6B08090528ADE25E 
[=]  ED1498E3089C72C68348D83CBD13F1247327BDBC9D75B09ECE3E051E19FE19BB 
[=]  98CB038757F2EDFD2DC5060D05C3296BC19A6F768290D555DFD50407E0E13A70 
                                                                      
[=] --- RDV4 RSA Public key --------------                            
[=] Len.................. 128                                         
[=] Exponent............. 010001                                      
[=] Public key modulus N                                              
[=]  E28D809BF323171D11D1ACA4C32A5B7E0A8974FD171E75AD120D60E9B76968FF 
[=]  4B0A6364AE50583F9555B8EE1A725F279E949246DF0EFCE4C02B9F3ACDCC623F 
[=]  9337F21C0C066FFB703D8BFCB5067F309E056772096642C2B1A8F50305D5EC33 
[=]  DB7FB5A3C8AC42EB635AE3C148C910750ABAA280CE82DC2F180F49F30A1393B5 
                                                                      
[+] RSA public key validation.... ( ok )                              
[+] RSA private key validation... ( ok )                              
[+] RSA verification..... ( ok )                                      
[+] Genuine Proxmark3 RDV4 signature detected                         
```

# backup first!
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To make a backup of the signature to file:

`mem dump -f flash_signature_dump -o 262015 -l 128`

