Kirk

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The PSP KIRK Crypto Engine is a security hardware device that is embedded into the TACHYON main IC chip. It is a bus master and can DMA to/from main DDR RAM memory, operating independantly of the CPU. It is intefaced via memory mapped registers at base of 0xBDE00000 (SPOCK Crypto Engine on the other hand is mapped to 0xBDF00000). It is capable of performing AES encryption, decryption, SHA1 Hash, pseudo random number generation, and signature generation and verifications (ECDSA) and CMAC.

Elliptic curves

The PSP uses ECDSA for public-key cryptography. Elliptic curves are known for being fast and only requiring small keys, contrary to other public-key cryptography algorithms. They are still considered to be very secure, even for the 160-bit curves used by the PSP, unless a mistake is made when using them.

These curves have been designed by Sony only for the console. They are not vulnerable to any known attack.

Both use the usual Weierstrass form.

Elliptic curve for CMD1

This curve is used for the ECDSA verification of CMD1. 

p = 0xFFFFFFFFFFFFFFFF0001B5C617F290EAE1DBAD8F
G = (0x2259ACEE15489CB096A882F0AE1CF9FD8EE5F8FA, 0x604358456D0A1CB2908DE90F27D75C82BEC108C0)
n = 0xFFFFFFFFFFFFFFFF00000001FFFFFFFFFFFFFFFF
a = -3
b = 0x65D1488C0359E234ADC95BD3908014BD91A525F9

The public key is hardcoded, and is equal to: (0xED9CE58234E61A53C685D64D51D0236BC3B5D4B9, 0x049DF1A075C0E04FB344858B61B79B69A63D2C39).

Elliptic curve for the other commands

This curved is used for Kirk commands 0xC, 0xD, 0x10, 0x11, and likely 0x12. 

p = 0xFFFFFFFFFFFFFFFEFFFFB5AE3C523E63944F2127
G = (0x128EC4256487FD8FDF64E2437BC0A1F6D5AFDE2C, 0x5958557EB1DB001260425524DBC379D5AC5F4ADF)
n = 0xFFFFFFFFFFFFFFFF00000001FFFFFFFFFFFFFFFF
a = -3
b = 0xA68BEDC33418029C1D3CE33B9A321FCCBB9E0F0B

The public key is variable. For the latest Pre-IPL version which add an additional ECDSA verification of the XOR of the block hashes, the public key is (0xBC660611A70BD7F2D140A48215C096D11D2D4112, 0xF0E9379AC4E0D387C542D091349DD15169DD5A87).

Code sample

Below is an example of how to manipulate these curves using the ecpy python library. 

import ecpy.curves

psp_curve_cmd1 = {
    'name':      "psp_curve_cmd1",
    'type':      "weierstrass",
    'size':      160,
    'field':     0xFFFFFFFFFFFFFFFF00000001FFFFFFFFFFFFFFFF,
    'generator': (0x2259ACEE15489CB096A882F0AE1CF9FD8EE5F8FA, 0x604358456D0A1CB2908DE90F27D75C82BEC108C0),
    'order':     0xFFFFFFFFFFFFFFFF0001B5C617F290EAE1DBAD8F,
    'cofactor':  1,
    'a':         -3,
    'b':         0x65D1488C0359E234ADC95BD3908014BD91A525F9,
}

psp_curve_cmd17 = {
    'name':      "psp_curve_cmd17",
    'type':      "weierstrass",
    'size':      160,
    'field':     0xFFFFFFFFFFFFFFFF00000001FFFFFFFFFFFFFFFF,
    'generator': (0x128EC4256487FD8FDF64E2437BC0A1F6D5AFDE2C, 0x5958557EB1DB001260425524DBC379D5AC5F4ADF),
    'order':     0xFFFFFFFFFFFFFFFEFFFFB5AE3C523E63944F2127,
    'cofactor':  1,
    'a':         -3,
    'b':         0xA68BEDC33418029C1D3CE33B9A321FCCBB9E0F0B,
}

crv1 = ecpy.curves.WeierstrassCurve(psp_curve_cmd1)
crv17 = ecpy.curves.WeierstrassCurve(psp_curve_cmd17)

pt1 = ecpy.curves.Point(0xED9CE58234E61A53C685D64D51D0236BC3B5D4B9, 0x049DF1A075C0E04FB344858B61B79B69A63D2C39, crv1)
pt17 = ecpy.curves.Point(0xbc660611a70bd7f2d140a48215c096d11d2d4112, 0xf0e9379ac4e0d387c542d091349dd15169dd5a87, crv17)

# verify the KIRK1 ECDSA private key
crv1_g = ecpy.curves.Point(0x2259ACEE15489CB096A882F0AE1CF9FD8EE5F8FA, 0x604358456D0A1CB2908DE90F27D75C82BEC108C0, crv1)
assert(crv1.mul_point(crv1.generator, 0xF392E26490B80FD889F2D9722C1F34D7274F983D) == pt1)

Commands

On PSP there are 18 KIRK commands. On PSVita, there are these 18 commands plus some new commands to support bigger keys (192 bits for example). See F00D commands.

KIRK functions are called with the same 5 arguments (outbuf, outbuf_size, inbuf, inbuf_size, service_number (which is the command ID)). Depending on the service number used, the expectations of the inbuf or outbuf vary and are detailed below.

Table

Command ID Name Short description Input size Output size Result Used in
1 KIRK_CMD_DECRYPT_PRIVATE Super-Duper decryption (no inverse) buf_size+0x40 buf_size memlmd, mesg_led
2 KIRK_CMD_2 Encrypt Operation (inverse of cmd 3)
3 KIRK_CMD_3 Decrypt Operation (inverse of cmd 2)
4 KIRK_CMD_ENCRYPT_IV_0 Encrypt Operation (inverse of cmd 7) (IV=0) buf_size+0x14 buf_size+0x14 chnnlsv, memab
5 KIRK_CMD_ENCRYPT_IV_FUSE Encrypt Operation (inverse of cmd 8) (IV=FuseID) buf_size+0x14 buf_size+0x14 chnnlsv, psheet since PSP FW 2.81 for PGD, ?openpsid for IDS Certificates?
6 KIRK_CMD_ENCRYPT_IV_USER Encrypt Operation (inverse of cmd 9) (IV=UserDefined)
7 KIRK_CMD_DECRYPT_IV_0 Decrypt Operation (inverse of cmd 4) (IV=0) buf_size+0x14 buf_size+0x14 memlmd, mesg_led,chnnlsv, memab
8 KIRK_CMD_DECRYPT_IV_FUSE Decrypt Operation (inverse of cmd 5) (IV=FuseID) buf_size+0x14 buf_size+0x14 chnnlsv, psheet since PSP FW 2.81 for PGD
9 KIRK_CMD_DECRYPT_IV_USER Decrypt Operation (inverse of cmd 6) (IV=UserDefined)
10 (0xA) KIRK_CMD_PRIV_SIGVRY Private Signature Verify (checks for private SCE sig)
11 (0xB) KIRK_CMD_HASH SHA1 Hash buf_size >= 0x14 ?0x14? memlmd, mesg_led, memab
12 (0xC) KIRK_CMD_MUL1 ECDSA Generate Keys 0 0x3C memab
13 (0xD) KIRK_CMD_MUL2 ECDSA Multiply Point 0x3C 0x3C
14 (0xE) KIRK_CMD_PRNGEN Pseudo Random Number Generation 0 0x14 mesg_led, chnnlsv, memab, semawm
15 (0xF) KIRK_CMD_15 (absolutely no idea – could be KIRK initialization) IPL
16 (0x10) KIRK_CMD_SIGGEN ECDSA Signature Generation 0x34 0x28 memab
17 (0x11) KIRK_CMD_SIGVRY Signature Verification (checks for generated signatures) 0x64 0 memab
18 (0x12) KIRK_CMD_CERTVRY Certificate Verification (IDStorage Certificates CMAC) 0xB8 0 openpsid, memab

Command 1: decryption and authentication

Overview

This function is used to both decrypt and verify the signature of the IPL blocks.

There are two versions of this service: AES CMAC Verification, and ECDSA Verification. They use the header section of the input buffer slightly differently.

In both cases, the total header length is 0x90. The first 0x60 bytes depend on the version. The last 0x30 bytes are the same in both cases:

Metadata Header Structure (Length 0x30):

Address Size Description
0x60 4 Set to 1
0x64 4 0 indicates AES CMAC version, 1 indicates ECDSA version
0x68 4 0
0x6C 4 0 for retail version and 0xFFFFFFFF for dev versions
0x70 4 Length of decrypted data
0x74 4 Length of the padding after the header and before the real data
0x78 8 0

AES CMAC Version

Key Header Structure (Length 0x60):

Address Size Description
0x00 16 Decryption key, encrypted with the KIRK1 AES master key
0x10 16 CMAC key, encrypted with the KIRK1 AES master key
0x20 16 Header hash (CMAC)
0x30 16 Data hash (CMAC)
0x40 32 0

Decryption process

The first 0x20 bytes of the Key Header are decrypted with the KIRK 1 Stored AES Key. This was allegedly discovered by Datel by decapping the chip and reversing engineering the algorithms and keys. This was also recovered through the failure in PS3 cryptography by decrypting the isolated module in the PSP emulator on the PS3.

The first block is the AES Key used for decrypting the main data. The second block is used to decrypt the next two blocks (0x20 bytes at offset 0x20). These represent the Metadata Header CMAC and the Data CMAC. They are checked against the AES CMAC of the header section and the AES CMAC of the data section.

ECDSA Version

Key Header Structure (Length 0x60):

Address Size Description
0x00 16 Decryption key, encrypted with the KIRK1 AES master key
0x10 16 Header ECDSA signature r
0x24 16 Header ECDSA signature s
0x38 16 Data ECDSA signature r
0x4C 16 Data ECDSA signature s

Decryption process

The ECDSA version is slightly different. Only the first block (0x10 bytes) is decrypted with the Kirk 1 AES Key. It is used to decrypt the main data section just as in the AES CMAC version. Rather than a CMAC, the Metadata header is checked by SHA1 hashing its 0x30 bytes and checking the signature components through a ECDSA Verify call. The encrypted Data section is also checked via SHA1 of the entire data through a ECDSA Verify call.

The ECDSA curve parameters are indicated above.

Command 2 (DRM encrypt)

This command is mostly unknown. The input data passed to KIRK is first checked (presumably CMAC), then decrypted, and re-encrypted with the console unique private key. Having that common key would allow legit creation of DRM BB install packages.

Command 3

Command 4

Command 5

Command 6

Command 7

Command 8

Command 9

Command 10

Command 11

Command 12: ECDSA key pair generation

Elliptic Curve Math formula : <math>y^2 = x^3 +ax +b mod p</math> with NP points on the curve

p = FFFFFFFFFFFFFFFF00000001FFFFFFFFFFFFFFFF

N= FFFFFFFFFFFFFFFEFFFFB5AE3C523E63944F2127

a= -3

b= A68BEDC33418029C1D3CE33B9A321FCCBB9E0F0B

Base Point:

Gx= 128EC4256487FD8FDF64E2437BC0A1F6D5AFDE2C

Gy= 5958557EB1DB001260425524DBC379D5AC5F4ADF

Invocation: 

u8 keypair[0x3c]
sceUtilsBufferCopyWithRange(keypair,0x3c,0,0,0xC);

This returns the following into the keypair buffer (each value is 0x14 bytes long):

  • 0x00 - randomly generated private key
  • 0x14 - Public Key point x value
  • 0x28 - Public Key point y value

Basically function 0xC generates a random number < N and multiplies it to the base point G to get the new public key.

Command 13: point multiplication

Elliptic Curve Math formula : <math>y^2 = x^3 +ax +b mod p</math> with NP points on the curve

p = FFFFFFFFFFFFFFFF00000001FFFFFFFFFFFFFFFF

NP= FFFFFFFFFFFFFFFEFFFFB5AE3C523E63944F2127

a= -3

b= A68BEDC33418029C1D3CE33B9A321FCCBB9E0F0B

Base Point:

Gx= 128EC4256487FD8FDF64E2437BC0A1F6D5AFDE2C

Gy= 5958557EB1DB001260425524DBC379D5AC5F4ADF

Invocation: 

u8 buffer[0x3C]
u8 newpoint[0x28]
memcpy(buffer, multiplier, 0x14);
memcpy(buffer+0x14, pointx, 0x14);
memcpy(buffer+0x28, pointy, 0x14);
sceUtilsBufferCopyWithRange(newpoint,0x28,buffer,0x3c,0xD);

The result is a new point(x and y are each 0x14 bytes long).

To test this, you can call 0xC service and copy the first 0x14 bytes to a new buffer, then copy the Gx and Gy values after that. Calling 0xD with the new buffer will return the values of x and y that were generated by the 0xC call.

Command 14

Command 15

Command 16

Command 17

Command 18

Library

Calling commands using KIRK registers

Notes

In 2008 SilverSpring wrote: 

Currently what is known about the cipher is that it is:
a block cipher operating in CBC mode
an all zero 128-bit initialization vector
128-bit block and key sizes
cmd4/7 uses a static key that is identical in all PSP’s
cmd5/8 uses a key based off the fuseID making all operations unique per PSP
cmd6/9 uses a user-defined 128-bit key
cmd1/2/3 uses the block cipher but also signature algorithms
the remaining KIRK cmd’s do not use the block cipher (sig, hash, & prng algo’s)
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