Certificate chains are intensively used to sign stuff on the Wii. They are normally preceded by a TMD file or a Ticket and are used to verify their signature up to the root key. Most chains contain three certificates, each padded to 0x40.
Certificates are also used to sign game savedata that is copied to the SD card. Saves are signed by Root-CA00000001-MS00000002-NGxxxxxxxx-AP0000000100000002 where AP is the system menu application cert (ECC/ECC public key), NG the device specific cert (ECC/ECC public key).
|Certificate||Signature type||Public key type||Cert name||Description|
|Root||RSA-4096||RSA-4096||Root||Root certificate stored in the IOS kernel, in the IOSC section|
|CA||RSA-4096||RSA-2048||CA00000001||Used to verify XS, CP, MS certs (issued by Root)|
|CA||RSA-4096||RSA-2048||CA00000002||Unused? (issued by Root)|
|Ticket||RSA-2048||RSA-2048||XS00000003||Used to verify retail tickets (issued by Root-CA00000001)|
|Ticket||RSA-2048||RSA-2048||XS00000006||Used to verify dev tickets (issued by Root-CA00000001)|
|TMD||RSA-2048||RSA-2048||CP00000004||Used to verify TMDs (issued by Root-CA00000001)|
|Device cert issuer||RSA-2048||ECC-B233||MS00000002||Used to verify device certificates (issued by Root-CA00000001)|
|Device cert issuer||RSA-2048||ECC-B233||MS00000003||Unused? (issued by Root-CA00000001)|
|Device cert||ECC-B233||ECC-B233||NG%08x (device ID)||Used to verify AP certs (issued by Root-CA00000001-MS00000002)|
|Application||ECC-B233||ECC-B233||AP%016lx (title ID)||Used to verify savedata (issued by Root-CA00000001-MS00000002-NG%08x)|
Because each certificate is used to sign another certificate or the TMD/Ticket and also is signed by another certificate or the root key each certificate has a child and a parent certificate.
To get the parent issuer name of a certificate just cut off everything after the last "-" of the issuer name. If this issuer name is "Root" the root key is used to sign the certificate otherwise another certificate in the chain is used.
To get the child you have to append a "-" and the stored child identity to the issuer name. If the child is not in the certificate chain the certificate is used to sign the TMD/Ticket (which will contain the child's name in its issuer field).
The TMD/Ticket is therefore effectively signed by the root key because if any of the certificates is modified some signature check will fail and the IOS will know that you changed something.
The following signature types may be used by a certificate:
|Type||Name||Signature Length (x)|
|0x00010002||Elliptic Curve||2*30 = 60 = 0x3c|
The following key types may be used by a certificate:
|Type||Name||Length (y) = Modulus + Public Exponent + (Pad to 0x40)|
|0x00000000||RSA-4096||0x200 + 0x4 + 0x38|
|0x00000001||RSA-2048||0x100 + 0x4 + 0x38|
|0x00000002||ECC-B233||60 + 0 + 60|
Each certificate in the chain has the following structure (padded to 0x40). Because the offsets and lengths of the data varies depending on the signature and key length the letter "x" represents the signature length, and the letter "y" represents the key length here:
|0x004||x||Signature of the data after the issuer by the parent's key|
|0x040 + x||64||Issuer|
|0x080 + x||4||Key type|
|0x084 + x||64||Child Certificate Identity|
|0x0c4 + x||y||Public Key (see Key Types)|