Kirk

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.

Invocation

All of the Kirk commands can be used using the function sceUtilsBufferCopyWithRange, which takes five arguments:

• the output buffer
• the output buffer size
• the input buffer (if there is one, NULL otherwise)
• the input buffer size (if there is one, 0 otherwise)
• the index of the command (as detailed below).

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	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 metadata header section and the AES CMAC of the whole data, from the metadata header section to the end of the data (including padding in-between).

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 & 3: DRM encrypt & decrypt

These commands are mostly unknown. In command 2, 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 is the decryption counterpart of command 2.

Commands 4 & 7: AES encrypt & decrypt, IV=0

These commands are used for encryption & decryption using a set of keys, all of which are available on the Keys page.

In both cases, data is prefixed with a 0x14-byte long header:

Address	Size	Description
0x00	4	Mode: must be 4 for encryption, 5 for decryption
0x04	8	Unknown (maybe used for commands 5/6/8/9?)
0x0C	4	Keyseed: index of the key to use, between 0x00 and 0x7F included
0x10	4	Size of the following data

A simple AES128-CBC encryption/decryption with an IV equal to 0 is applied on the rest of the data.

Commands 5 & 6 & 8 & 9: AES encrypt & decrypt, IV!=0

These commands are supposed to be similar to commands 4 & 7, but with different IVs. They might use the same header. The keys might also be different. Commands 5/8 use a key based off the fuseID making all operations unique per PSP, while commands 6/9 use a user-defined 128-bit key.

This needs testing!

Command 12: ECDSA key pair generation

This command generates a random private key and computes the associated public key. See above for the parameters of the elliptic curve.

This returns the following into the keypair buffer, of size 0x3C (each value is 0x14 bytes long):

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

Command 13: point multiplication

This command multiplies an elliptic curve point by a scalar. See above for the parameters of the elliptic curve.

Input (size 0x3c):

• 0x00 - scalar k
• 0x14 - point x value P.x
• 0x28 - point y value P.y

Output (size 0x28):

• 0x00 - point x value (kP).x
• 0x14 - point y value (kP).y

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

Library

Calling commands using KIRK registers

• [1]

• [2]

• [3]

• [4]