Archived
TD0048: Curve25519 Implementations in FDP_DAR_EXT.2.2 Requirement
Publication Date
2015.06.16
Protection Profiles
PP_MD_v2.0
Other References
PP_MDF_V2.0, requirement FDP_DAR_EXT.2.2
Issue Description
Curve25519 implementations are becoming more prevalent for a variety of functionality. One use in mobile devices is for the encryption of sensitive data files that are open and writable when the device is locked (lock-screen DAR). Several customers expressed desire to use this functionality. The current MDF PP, however, does not allow this curve and therefore there is no way to use this functionality and maintain the mobile device in its evaluated configuration. Resolution
Add wording to the FCS_CKM.1.1(1) requirement to include the Curve25519 option and ensure this is referred to in FDP_DAR_EXT.2.2. FCS_CKM.1.1(1) … - [ECC schemes] using [selection: [“NIST curves” P-256, P-384 and [selection: P-521, no other curves] that meet the following: [FIPS PUB 186-4, “Digital Signature Standard (DSS)”, Appendix B.4]], [Curve25519 schemes that meet the following: [IETF draft-irtf-cfrg-curves, "Elliptic Curves for Security"]]];
The evaluator shall ensure that the TSS identifies the key sizes supported by the TOE. If the ST specifies more than one scheme, the evaluator shall examine the TSS to verify that it identifies the usage for each scheme. The evaluator shall verify that the AGD guidance instructs the administrator how to configure the TOE to use the selected key generation scheme(s) and key size(s) for all uses defined in this PP.
The evaluator shall verify the implementation of RSA Key Generation by the TOE using the Key Generation test. This test verifies the ability of the TSF to correctly produce values for the key components including the public verification exponent Key Pair generation specifies 5 ways (or methods) to generate the primes 1. Random Primes: - Provable primes
- Probable primes
2. Primes with Conditions: - Primes
*p1, p2, q1,q2, p*and*q*shall all be provable primes - Primes
*p1, p2, q1*, and*q2*shall be provable primes and*p*and*q*shall be probable primes - Primes
*p1, p2, q1,q2, p*and*q*shall all be probable primes
To test the key generation method for the Random Provable primes method and for all the Primes with Conditions methods, the evaluator must seed the TSF key generation routine with sufficient data to deterministically generate the RSA key pair. This includes the random seed(s), the public exponent of the RSA key, and the desired key length. For each key length supported, the evaluator shall have the TSF generate 25 key pairs. The evaluator shall verify the correctness of the TSF’s implementation by comparing values generated by the TSF with those generated from a known good implementation. If possible, the Random Probable primes method should also be verified against a known good implementation as described above. Otherwise, the evaluator shall have the TSF generate 10 keys pairs for each supported key length nlen and verify: - n = p*q,
- p and q are probably prime according to Miller-Rabin tests,
- GCD(p-1,e) = 1,
- GCD(q-1,e) = 1,
- 2^16 <= e <= 2^256 and e is an odd integer,
- |p-q| > 2^(nlen/2 - 100),
- p >= squareroot(2)*( 2^(nlen/2 -1) ),
- q >= squareroot(2)*( 2^(nlen/2 -1) ),
- 2^(nlen/2) < d < LCM(p-1,q-1),
- e*d = 1 mod LCM(p-1,q-1).
If the TSF implements the ANSI X9.311998 scheme, the evaluator shall check to ensure that the TSS describes how the keypairs are generated. In order to show that the TSF implementation complies with ANSI X9.311998, the evaluator shall ensure that the TSS contains the following information: - The TSS shall list all sections of the standard to which the TOE complies;
- For each applicable section listed in the TSS, for all statements that are not "shall" (that is, "shall not", "should", and "should not"), if the TOE implements such options it shall be described in the TSS. If the included functionality is indicated as "shall not" or "should not" in the standard, the TSS shall provide a rationale for why this will not adversely affect the security policy implemented by the TOE;
? For each applicable section of Appendix B, any omission of functionality related to "shall" or “should” statements shall be described.
For each supported NIST curve, i.e., P-256, P-384 and P-521, the evaluator shall require the implementation under test (IUT) to generate 10 private/public key pairs. The private key shall be generated using an approved random bit generator (RBG). To determine correctness, the evaluator shall submit the generated key pairs to the public key verification (PKV) function of a known good implementation.
For each supported NIST curve, i.e., P-256, P-384 and P-521, the evaluator shall generate 10 private/public key pairs using the key generation function of a known good implementation and modify five of the public key values so that they are incorrect, leaving five values unchanged (i.e., correct). The evaluator shall obtain in response a set of 10 PASS/FAIL values.
The evaluator shall require the implementation under test (IUT) to generate 10 private/public key pairs. The private key shall be generated as specified in IETF draft-irtf-cfrg-curves, "Elliptic Curves for Security" using an approved random bit generator (RBG). To determine correctness, the evaluator shall submit the generated key pairs to the public key verification (PKV) function of a known good implementation.
[Note: We are assuming the PKV function of the good implementation will: (a) confirm the private and public keys are 32-byte values (b) confirm the three least significant bits of the least significant byte of the private key are zero (c) confirm the most significant bit of the most significant byte is zero (d) confirm the second most significant bit of the most significant byte is one (e) calculate the expected public key from the private key and confirm it matches the supplied public key ] The evaluator shall generate 10 private/public key pairs using the key generation function of a known good implementation and modify 5 of the public key values so that they are incorrect, leaving five values unchanged (i.e., correct). The evaluator shall obtain in response a set of 10 PASS/FAIL values.
The evaluator shall verify the implementation of the Parameters Generation and the Key Generation for FFC by the TOE using the Parameter Generation and Key Generation test. This test verifies the ability of the TSF to correctly produce values for the field prime p, the cryptographic prime q (dividing p-1), the cryptographic group generator g, and the calculation of the private key x and public key y. The Parameter generation specifies 2 ways (or methods) to generate the cryptographic prime q and the field prime p: Cryptographic and Field Primes: - Primes q and p shall both be provable primes
- Primes q and field prime p shall both be probable primes
and two ways to generate the cryptographic group generator g: Cryptographic Group Generator: - Generator g constructed through a verifiable process
- Generator g constructed through an unverifiable process.
The Key generation specifies 2 ways to generate the private key x: Private Key: - len(q) bit output of RBG where 1 <=x <= q-1
- len(q) + 64 bit output of RBG, followed by a mod q-1 operation where 1<= x<=q-1.
The security strength of the RBG must be at least that of the security offered by the FFC parameter set. To test the cryptographic and field prime generation method for the provable primes method and/or the group generator g for a verifiable process, the evaluator must seed the TSF parameter generation routine with sufficient data to deterministically generate the parameter set. For each key length supported, the evaluator shall have the TSF generate 25 parameter sets and key pairs. The evaluator shall verify the correctness of the TSF’s implementation by comparing values generated by the TSF with those generated from a known good implementation. Verification must also confirm - g != 0,1
- q divides p-1
- g^q mod p = 1
- g^x mod p = y
for each FFC parameter set and key pair.
*[***RSA-based key establishment schemes**] that meets the following: [**NIST Special Publication 800-56B, “Recommendation for Pair-Wise Key Establishment Schemes Using Integer Factorization Cryptography”**];
*[***Elliptic curve-based key establishment schemes**] that meets the following: [selection:*NIST Special Publication 800-56A, “Recommendation for Pair-Wise Key Establishment Schemes Using Discrete Logarithm Cryptography”;**IETF draft-irtf-cfrg-curves, "Elliptic Curves for Security"**];*
*[***Finite field-based key establishment schemes**] that meets the following: [**NIST Special Publication 800-56A, “Recommendation for Pair-Wise Key Establishment Schemes Using Discrete Logarithm Cryptography”**];
] for the purposes of encrypting sensitive data received while the device is locked.
The RSA-based key establishment schemes are described in Section 9 of NIST SP 800-56B; however, Section 9 relies on implementation of other sections in SP 800-56B. If the TOE acts as a receiver in the RSA key establishment scheme, the TOE does not need to implement RSA key generation. The elliptic curves used for the key establishment scheme shall correlate with the curves specified in FCS_CKM.1.1(1). The domain parameters used for the finite field-based key establishment scheme are specified by the key generation according to FCS_CKM.1.1(1).
The evaluator shall ensure that the supported key establishment schemes correspond to the key generation schemes identified in FCS_CKM.1.1(1). If the ST specifies more than one scheme, the evaluator shall examine the TSS to verify that it identifies the usage for each scheme. The evaluator shall verify that the AGD guidance instructs the administrator how to configure the TOE to use the selected key establishment scheme(s).
The evaluator shall verify the implementation of the key establishment schemes supported by the TOE using the applicable tests below.
The evaluator shall verify a TOE's implementation of SP800-56A key agreement schemes using the following Function and Validity tests. These validation tests for each key agreement scheme verify that a TOE has implemented the components of the key agreement scheme according to the specifications in the Recommendation. These components include the calculation of the DLC primitives (the shared secret value Z) and the calculation of the derived keying material (DKM) via the Key Derivation Function (KDF). If key confirmation is supported, the evaluator shall also verify that the components of key confirmation have been implemented correctly, using the test procedures described below. This includes the parsing of the DKM, the generation of MACdata and the calculation of MACtag.
The Function test verifies the ability of the TOE to implement the key agreement schemes correctly. To conduct this test the evaluator shall generate or obtain test vectors from a known good implementation of the TOE supported schemes. For each supported key agreement scheme-key agreement role combination, KDF type, and, if supported, key confirmation role- key confirmation type combination, the tester shall generate 10 sets of test vectors. The data set consists of one set of domain parameter values (FFC) or the NIST approved curve (ECC) per 10 sets of public keys. These keys are static, ephemeral or both depending on the scheme being tested.
The evaluator shall obtain the DKM, the corresponding TOE’s public keys (static and/or ephemeral), the MAC tag(s), and any inputs used in the KDF, such as the Other Information field OI and TOE id fields. If the TOE does not use a KDF defined in SP 800-56A, the evaluator shall obtain only the public keys and the hashed value of the shared secret. The evaluator shall verify the correctness of the TSF’s implementation of a given scheme by using a known good implementation to calculate the shared secret value, derive the keying material DKM, and compare hashes or MAC tags generated from these values. If key confirmation is supported, the TSF shall perform the above for each implemented approved MAC algorithm.
The Validity test verifies the ability of the TOE to recognize another party’s valid and invalid key agreement results with or without key confirmation. To conduct this test, the evaluator shall obtain a list of the supporting cryptographic functions included in the SP800-56A key agreement implementation to determine which errors the TOE should be able to recognize. The evaluator generates a set of 24 (FFC) or 30 (ECC) test vectors consisting of data sets including domain parameter values or NIST approved curves, the evaluator’s public keys, the TOE’s public/private key pairs, MACTag, and any inputs used in the KDF, such as the other info and TOE id fields.
The evaluator shall inject an error in some of the test vectors to test that the TOE recognizes invalid key agreement results caused by the following fields being incorrect: the shared secret value Z, the DKM, the other information field OI, the data to be MACed, or the generated MACTag. If the TOE contains the full or partial (only ECC) public key validation, the evaluator will also individually inject errors in both parties’ static public keys, both parties’ ephemeral public keys and the TOE’s static private key to assure the TOE detects errors in the public key validation function and/or the partial key validation function (in ECC only). At least two of the test vectors shall remain unmodified and therefore should result in valid key agreement results (they should pass). The TOE shall use these modified test vectors to emulate the key agreement scheme using the corresponding parameters. The evaluator shall compare the TOE’s results with the results using a known good implementation verifying that the TOE detects these errors.
The evaluator shall verify that the TSS describes whether the TOE acts as a sender, a recipient, or both for RSA-based key establishment schemes. If the TOE acts as a sender, the following assurance activity shall be performed to ensure the proper operation of every TOE supported combination of RSA-based key establishment scheme: To conduct this test the evaluator shall generate or obtain test vectors from a known good implementation of the TOE supported schemes. For each combination of supported key establishment scheme and its options (with or without key confirmation if supported, for each supported key confirmation MAC function if key confirmation is supported, and for each supported mask generation function if KTS-OAEP is supported), the tester shall generate 10 sets of test vectors. Each test vector shall include the RSA public key, the plaintext keying material, any additional input parameters if applicable, the MacKey and MacTag if key confirmation is incorporated, and the outputted ciphertext. For each test vector, the evaluator shall perform a key establishment encryption operation on the TOE with the same inputs (in cases where key confirmation is incorporated, the test shall use the MacKey from the test vector instead of the randomly generated MacKey used in normal operation) and ensure that the outputted ciphertext is equivalent to the ciphertext in the test vector. If the TOE acts as a receiver, the following assurance activities shall be performed to ensure the proper operation of every TOE supported combination of RSA-based key establishment scheme: To conduct this test the evaluator shall generate or obtain test vectors from a known good implementation of the TOE supported schemes. For each combination of supported key establishment scheme and its options (with our without key confirmation if supported, for each supported key confirmation MAC function if key confirmation is supported, and for each supported mask generation function if KTS-OAEP is supported), the tester shall generate 10 sets of test vectors. Each test vector shall include the RSA private key, the plaintext keying material (KeyData), any additional input parameters if applicable, the MacTag in cases where key confirmation is incorporated, and the outputted ciphertext. For each test vector, the evaluator shall perform the key establishment decryption operation on the TOE and ensure that the outputted plaintext keying material (KeyData) is equivalent to the plaintext keying material in the test vector. In cases where key confirmation is incorporated, the evaluator shall perform the key confirmation steps and ensure that the outputted MacTag is equivalent to the MacTag in the test vector. The evaluator shall ensure that the TSS describes how the TOE handles decryption errors. In accordance with NIST Special Publication 800-56B, the TOE must not reveal the particular error that occurred, either through the contents of any outputted or logged error message or through timing variations. If KTS-OAEP is supported, the evaluator shall create separate contrived ciphertext values that trigger each of the three decryption error checks described in NIST Special Publication 800-56B section 7.2.2.3, ensure that each decryption attempt results in an error, and ensure that any outputted or logged error message is identical for each. If KTS-KEM-KWS is supported, the evaluator shall create separate contrived ciphertext values that trigger each of the three decryption error checks described in NIST Special Publication 800-56B section 7.2.3.3, ensure that each decryption attempt results in an error, and ensure that any outputted or logged error message is identical for each.
The evaluator shall verify a TOE's implementation of the key agreement scheme using the following Function and Validity tests. These validation tests for each key agreement scheme verify that a TOE has implemented the components of the key agreement scheme according to the specification. These components include the calculation of the shared secret K and the hash of K
The Function test verifies the ability of the TOE to implement the key agreement schemes correctly. To conduct this test the evaluator shall generate or obtain test vectors from a known good implementation of the TOE supported schemes. For each supported key agreement role and hash function combination, the tester shall generate 10 sets of public keys. These keys are static, ephemeral or both depending on the scheme being tested.
The evaluator shall obtain the shared secret value K, and the hash of K. The evaluator shall verify the correctness of the TSF’s implementation of a given scheme by using a known good implementation to calculate the shared secret value K and compare the hash generated from this values.
The Validity test verifies the ability of the TOE to recognize another party’s valid and invalid key agreement results. To conduct this test, the evaluator generates a set of 30 test vectors consisting of data sets including the evaluator’s public keys and the TOE’s public/private key pairs.
The evaluator shall inject an error in some of the test vectors to test that the TOE recognizes invalid key agreement results caused by the following fields being incorrect: the shared secret value K or the hash of K. At least two of the test vectors shall remain unmodified and therefore should result in valid key agreement results (they should pass). The TOE shall use these modified test vectors to emulate the key agreement scheme using the corresponding parameters. The evaluator shall compare the TOE’s results with the results using a known good implementation verifying that the TOE detects these errors. Justification
These two new requirements allow additional elliptic curves to be used for sensitive data received while the device is locked. Because this data is not transmitted to other devices, interoperability is not required in this application. |