Keystone

This file is generated on app package generation based on the passcode provided. It is then included in every savedata and trophy created by the application.

It is used to prevent applications from mounting savedata of other applications, as you need to know at least the fingerprint to do it.

See also PS Vita Keystone.

PS4

Location

The keystone file is located in the sce_sys folder of every applications/patches/additional contents/savedata/trophies. It is PFS encrypted.

<save data directory>:/sce_sys/keystone

Structure

Size is always 96 bytes.

Offset	Size	Description	Notes
0x0	0x8	Magic	"keystone"
0x8	0x2	Type	always 2
0xA	0x2	Version	always 1
0xC	0x14	Padding	always zeroed
0x20	0x20	Passcode Digest	HMAC-SHA256 digest made with keystone_passcode_secret as key
0x40	0x20	Keystone Digest	HMAC-SHA256 digest made with keystone_ks_secret as key

Usage

Generation

SCE provides in official SDK a tool called pc2ks that converts a passcode to a keystone.

Below is a simple reimplementation of pc2ks in CSharp.

public static byte [] GenerateKeystoneFile (string passcode)
{
    // 1. The first 32 bytes are constant
    byte[] keystone = {
        0x6B, 0x65, 0x79, 0x73, 0x74, 0x6F, 0x6E, 0x65, 0x02, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00,
        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00
    };

    // 2. Convert the 32 characters of the passcode to a byte array
    byte[] passcodeInHEX = Encoding.ASCII.GetBytes(passcode);

    // 3. Calculate the fingerprint of the passcode
    HMACSHA256 hmac = new HMACSHA256();
    hmac.Key = keystone_passcode_secret;

    byte[] fingerprint = hmac.ComputeHash(passcodeInHEX);

    // 4. Concat the 32 bytes from point 1 and the 32 bytes from point 3
    keystone = keystone.Concat(fingerprint).ToArray();

    // 5. Calculate the SHA256Hmac of the 64 bytes from point 4
    hmac.Key = keystone_ks_secret;
    byte[] sha256hmac = hmac.ComputeHash(keystone);

    // 6. Concat the constant bytes from point 1, the fingerprint from point 3 and the hmac from point 5
    keystone = keystone.Concat(sha256hmac).ToArray();


    return keystone;

}

Verification

The first step is to check the Digest of the keystone file (using VerifyKeystone). The process is to use the keystone_ks_secret to check the keystone Digest at position 0x40 in the file.

If it is correct, it proceeds to check the passcode Digest, ?which is not present on retail units?. Use keystone_passcode_secret to calculate the digest of the passcode stored at offset 0x20.

Sample keystone file

Below is a sample keystone file created when provided a passcode consisting of all zeros "00000000000000000000000000000000":

The first 32 are constant:
00000000  6b 65 79 73 74 6f 6e 65  02 00 01 00 00 00 00 00  |keystone........|
00000010  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
Fingerprint of the passcode:
00000020  29 4a 5e d0 6d b1 70 61  8f 2e ed 8c 42 4b 9d 82  |)J^.m.pa....BK..|
00000030  88 79 c0 80 cc 66 fb c4  86 4f 69 e9 74 de b8 56  |.y...f...Oi.t..V|
SHA256Hmac of the first 64 bytes of the file:
00000040  fa 0d 0c 2e bd 6a 00 80  63 71 3d e8 81 0d 7e 10  |.....j..cq=...~.|
00000050  b7 32 14 3b 91 cd 2e 4f  ea 2d 20 53 10 6e b7 5d  |.2.;...O.- S.n.]|