Method and apparatus for two-step data signing
A system and method for signing data is presented. In one embodiment, the method comprises: generating a data signing key; transforming the data signing key into a first subkey and a second subkey; encrypting the first subkey according to a secret key of an ODSS; generating a signature verification public key; providing the signature verification public key, the encrypted first subkey, and the second subkey for storage in a client device; accepting a request to sign the data, the request having a representation of the data and the encrypted first subkey; generating a partially computed signature of the data according to the representation of the data and the encrypted first subkey; and providing the partially computed signature of the data to the client device.
1. A method comprising steps performed by a computer processor, the steps including:
(a) generating a key pair, the key pair including a data signing key and a signature verification public key;
(b) transforming the data signing key into a first subkey and a second subkey;
(c) encrypting the first subkey according to a secret key of an online data signing system (ODSS);
(d) providing the signature verification public key, the encrypted first subkey, and the second subkey to a client device for storage in the client device;
(e) accepting a request to sign data, the request comprising:
(1) a representation of the data to be signed; and
(2) the encrypted first subkey;
(f) generating a partially computed signature of the data according to the representation of the data and the encrypted first subkey; and
(g) providing the partially computed signature of the data to the client device.
2. The method of claim 1 , further comprising the client device computing a signature of the data using the provided partially computed signature.
3. The method of claim 1 , wherein the method further comprises encrypting the second subkey according to a secret key of the client device; and subsequently providing the signature verification public key, the encrypted first subkey, and the encrypted second subkey for storage in the client device.
4. The method of claim 1 , wherein the signature verification public key is provided to the client device as a digital certificate.
5. The method of claim 4 , further comprising transmitting the signature verification public key to a third party certificate authority and receiving the digital certificate from the third party certificate authority.
6. The method of claim 4 , wherein the digital certificate is attached to a signature of the data to generate a final signed data image.
7. The method of claim 1 , further comprising encrypting the data signing key and providing the encrypted data signing key to the client device for archival.
8. The method of claim 1 , wherein generating the partially computed signature of the data according to the representation of the data and the encrypted first subkey comprises decrypting the encrypted first subkey according to the secret key to recover the first subkey and generating the partially computed signature of the data according to the representation of the data and the first subkey.
9. The method of claim 1 , wherein:
(a) the method further comprises requesting the data signing key;
(b) the request for the data signing key is accepted from an administrator client device; and
(c) the request to sign the data is accepted from a user client device.
10. The method of claim 1 , wherein the representation of the data is selected from a group comprising the data and a digest of the data.
11. The method of claim 10 , wherein the data comprises one or more of a group comprising software code and a message having a set of debugging permissions and a device identifier for unlocking a specific device for debugging.
12. The method of claim 1 , wherein generating a partially computed signature comprises combining the representation of the data with additional data provided by the ODSS, to produce an augmented representation of the data and generating the partially computed signature according to the augmented representation of the data and the encrypted first subkey.
13. The method of claim 1 , wherein:
(a) the key pair is an RSA (Rivest-Shamir-Adleman) key pair;
(b) the data signing key has a private key exponent d; and
(c) transforming the data signing key into a first subkey and a second subkey comprises splitting the private key exponent d into s1 and s2 such that s1+s2≡d (mod φ(n)), where n is the RSA modulus and φ(n) is the Euler's totient function of n.
14. The method of claim 13 , wherein:
(a) the partially computed signature is generated as sign p =h(m) s1 mod n, wherein:
(1) h(m) is a digest of the data; and
(2) s1 is the first subkey;
(b) the method further comprises:
(1) computing a completely computed signature s according to s=(sign p ·(h(m) s2 mod n)) mod n, where s2 is the second subkey.
15. The method of claim 1 , wherein:
(a) the key pair is an RSA key pair;
(b) the data signing key has a private key exponent d; and
(c) transforming the data signing key into a first subkey and a second subkey comprises multiplicatively splitting the private key exponent d into s1 and s2, such that s1·s2 ≡d (mod φ(n)), where n is the RSA modulus and φ(n) is the Euler's totient function of n.
16. The method of claim 15 , wherein:
(a) the partially computed signature is generated as s P =h(m) s1 mod n, where
(1) h(m) is a digest of the data; and
(2) s1 is the first subkey;
(b) the method further comprises:
(1) the client device computing a completely computed signature s, according to s=(sign p s2 ) mod n, where s2 is the second subkey.
17. The method of claim 1 , further comprising installing the signature verification public key into a software platform for validating signatures generated with the first subkey and the second subkey.
18. The method of claim 1 , wherein:
(a) the step of providing the signature verification public key, the encrypted first subkey, and the second subkey to a client device comprises
encrypting the second subkey according to a secret key possessed by the client device
(b) the method further comprises
the client device decrypting the encrypted second subkey with the secret key possessed by the client device.
19. An apparatus, comprising:
(a) a processor;
(b) a memory, communicatively coupled to the processor, the memory storing processor instructions comprising processor instructions for:
(1) generating a key pair, the key pair including a data signing key and a signature verification public key;
(2) transforming the data signing key into a first subkey and a second subkey;
(3) encrypting the first subkey according to a secret key of an online data signing system (ODSS);
(4) providing the signature verification public key, the encrypted first subkey, and the second subkey to a client device for storage in the client device;
(5) accepting a request to sign data, the request comprising:
(i) a representation of the data to be signed; and
(ii) the encrypted first subkey;
(6) generating a partially computed signature of the data according to the representation of the data and the encrypted first subkey; and
(7) providing the partially computed signature of the data to the client device.