otptool - view and extract data from a 3DS OTP
otptool [-c ctcert_out] [-d decrypted_otp_out] [-Dh] otp
The otptool utility views and extracts data from a 3DS OTP dump. The dump can be either encrypted or already decrypted. If no arguments are given, no files will be written.
The options are as follows:
-c ctcert_out
Generate the CTCert from the OTP and write the CTCert to ctcert_out.
-d decrypted_otp_out
Write the decrypted OTP to decrypted_otp_out. Some utilities require a decrypted OTP, such as yellows8's boot9_aeskeytool_conunique.sh from boot9_tools.
-D
Use the development key and IV rather than the retail ones for decryption. This option is used to handle OTPs from development units.
The displayed fields mean:
Device ID
Every 3DS unit has a unique device identifier (ID). This is used, amongst other things, for the eShop infrastructure.
Fallback keyY
This data is used as fallback keyY data if nand:/private/movable.sed does not exist or is invalid. Internally, this is actually a series of two additional 64-bit console-unique IDs, but they are never used as such in practice.
Version
This specifies the OTP version. It seems that earlier versions of Nintendo's operating systems also had OTPs of some sort, hence the version field.
Is dev unit
If "true", this is a dev unit. If "false", this is not a dev unit. Note that this is separate from the decryption process – it's theoretically possible that an OTP uses dev encryption but then specifies a retail console, but has never been specified in the wild.
Manufactured
Date and time when this unit was manufactured/the OTP was written. The actual NAND flashing process and unit assembly may take place at a later time.
CTCert expiry
The CTCert can expire. The expiry time seems to be exactly 20 years after the manufacturing date as described above.
EC PrivKey
Private key for the sect233r1 elliptic curve. Seems to be specified as R followed by S in big-endian.
Signature
An ECDSA signature over the CTCert using curve sect233r1.
To build otptool, just type make. You require a POSIX-compatible environment for getopt(3). Additionally, you require libgcrypt at version 1.4.0 or above; otptool may work on lower versions, but this hasn't been tested.
The CTCert signature is not verified. As the OTP already has a hash that can be used to verify, it does not seem to be worthwhile.