NXP Semiconductors

High Tech Campus 60 AE Eindhoven 5656 NL +44 7889 488 335 cvvrede@gmail.com

IBM Research GmbH

Saeumerstrasse 4 Rueschlikon 8803 CH sid@zurich.ibm.com

IBM Research GmbH

Saeumerstrasse 4 Rueschlikon 8803 CH bhe@zurich.ibm.com

IBM Research GmbH

Saeumerstrasse 4 Rueschlikon 8803 CH tvi@zurich.ibm.com

IBM Research GmbH

Saeumerstrasse 4 Rueschlikon 8803 CH osb@zurich.ibm.com

Utimaco IS GmbH

Germanusstrasse 4 Aachen 52080 DE dieter.bong@utimaco.com

NXP Semiconductors

High Tech Campus 60 AE Eindhoven 5656 NL +44 7889 488 335 joppe.bos@nxp.com

General Internet Engineering Task Force template This proposal defines key management approaches for Quantum Safe Cryptographic (QSC) algorithms currently under evaluation in the NIST Post Quantum Cryptography (PQC) process. This includes key identification, key serialization, and key compression. The purpose is to provide guidance such that the adoption of quantum-safe algorithms is not hampered with the fragmented evolution of necessary key management standards. Early definition of key material standards will help expedite the adoption of new quantum safe algorithms at the same time as improving interoperability between implementations and minimizing divergence across standards.

Introduction QSC algorithms being standardized in the NIST PQC Process have evolved through several rounds and iterations. Keys are neither easily identifiable nor compatible across rounds. It is also expected that algorithms will evolve after final candidates have been selected. The lack of binary compatibility between algorithm versions and variants means that it is important to clearly identify key material. Parallel to the NIST process, industry is evaluating the impact of adopting new PQC algorithms, in particular key management. Here it is important to define and standardize key serialization and encoding formats. Finally, we have seen that many platforms and protocols are very constrained when it comes to the amount of memory or space available for key objects. This makes it important to define and standardize key compression formats. This proposal addresses aspects of key identification, key serialization, and key compression for NIST PQC candidates.

Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 .

Algorithm Identification Algorithm identification is important for several reasons:

• Managing a smooth transition from early adoption algorithm versions to production versions where there is no compatibility.
• Supporting different algorithm versions from different NIST rounds
• Identifying different key serialization strategies
• Identifying compressed and uncompressed keys

The current standardization of quantum-safe algorithms does not address the definition of serialization structures for keys. As a result, it has become commonplace for the cryptographic community working on and with these algorithms to define their own approaches. This leads to proprietary and internal representations for key material. This has certain advantages in terms of ease of experimentation while focusing on finding the best-performing QSC algorithms. In terms of longer-term support where algorithm versions change this is a problem. For the purpose of temporarily supporting ongoing experimentation with opaque blobs, for example in simple "classic key-emulating" test applications, such as TLS, this document specifies a temporary but suboptimal key format in section 2.1, mainly to establish a base of reference for as long as experimentation is ongoing. This is referenced as the 'raw key material' representation. At the same time, this proposal documents in section 2.2 below, a long-term key representation format useful to address the goals outlined in 1.1. This proposal contains all information required to document and transition from one version of key material representation to another.

Algorithm and Algorithm Parameter Object Identifier Algorithm and algorithm parameter information shall have ASN.1 type AlgorithmIdentifier as given in and shall be extended by an pqcAlgorithmParameterName type in the optional parameters field:

Overview of PQC algorithm and parameter OIDs Each PQC algorithm has its own specific parameters. Different parameter sets provide different levels of security within one algorithm. This memo attributes a name and an OID to the different security level NIST round 3 parameter sets. The following table gives an overview of the possible OIDs in the algorithm field and possible parameters set names in the parameters field of the AlgorithmIdentifier type. Each name or OID represents a single parameter set of given security. Details can be found in the individual PQC algorithm chapters.

Key Formats The private key format defined is from PKCS#8 . PKCS#8 PrivateKeyInfo is defined as: Distributing a PQC private key requires a PKCS#8 PrivateKeyInfo with a joined PQC algorithm and algorithm parameter OID in the algorithm field of AlgorithmIdentifier and a PQC algorithm specific private key object in the privateKey field of PrivateKeyInfo. Both objects are defined in the specific algorithm sections of this document. For an overview see tables above and below.

Public Key Format based on RFC5280 subjectPublicKeyInfo is defined in as: Distributing a PQC public key requires a subjectPublicKeyInfo with a joined PQC algorithm and algorithm parameter OID in the algorithm field of AlgorithmIdentifier and a PQC algorithm specific public key object in the subjectPublicKey field of subjectPublicKeyInfo. Both objects are defined in the specific algorithm sections of this document. For an overview see tables above and below.

Overview of Memo Definitions - PQC Key Formats The privateKey field in the PrivateKeyInfo type is an OCTET STRING whose contents are the value of the private key. The interpretation of the content differs from PQC algorithm to algorithm. The subjectPublicKey field in the subjectPublicKeyInfo type RFC 5480 is a BIT STRING whose contents are the value of the public key. Here also the interpretation of the content differs from PQC algorithm to algorithm. For an NTRU private key, for example, the content needs to be interpreted according to the NTRUPrivateKey type and for an NTRU public key the content needs to be interpreted according to the NTRUPublicKey type; both are defined in the NTRU chapter below.

Classic McEliece Classic McEliece is an IND-CCA2-secure key encapsulation mechanism (KEM). The KEM is built conservatively from a PKE designed for OW-CPA security, namely Niederreiter's dual version of McEliece's PKE using binary Goppa codes. Project Website: https://classic.mceliece.org/index.html NIST Round 3 Submission: https://csrc.nist.gov/CSRC/media/Projects/post-quantum-cryptography/documents/round-3/submissions/Classic-McEliece-Round3.zip

Algorithm Parameter Identifiers Classic McEliece uses OIDs to identify parameters sets for different security strengths.

Key Details Public key. The public-key consists of

• T: mt x k matrix

Each row of T is represented as a ceiling(k/8)-byte string, and the public key is represented as the mt*ceiling(k/8)-byte concatenation of these strings. Private key. The private key consists of five parameters:

• delta: nonce
• C : column selections
• g : monic irreducible polynomial
• alpha: field orderings
• s : uniform random n-bit string

The size necessary to hold all private key elements accounts to ceiling(l / 8) + [ceiling(nu / 8) | 8] + ceiling(m / 8) + ceiling((2*m - 1) * 2*m - 4) + ceiling(n / 8) bytes. The resulting public key and private key sizes can be found in the table below.

Private Key Full Encoding Distributing a Classic McEliece private key with PKCS#8 involves including:

• mceliece{n}{t}[f]-r3 in the algorithm field of AlgorithmIdentifier
• McEliecePrivateKey in the privateKey field, which is an OCTET STRING.

When a Classic McEliece public key is included in the distributed PrivateKeyInfo, the PublicKey field in McEliecePrivateKey is used (see description of McEliecePublicKey below). ASN.1 Encoding for a Classic McEliece private key for fully populated:

Public Key Full Encoding

Kyber Kyber is an IND-CCA2-secure key encapsulation mechanism (KEM), whose security is based on the hardness of solving the learning-with-errors (LWE) problem over module lattices. Project Website: https://pq-crystals.org/kyber/index.shtml NIST Round 3 Submission: https://csrc.nist.gov/CSRC/media/Projects/post-quantum-cryptography/documents/round-3/submissions/Kyber-Round3.zip

Algorithm Parameter Identifiers Kyber uses OIDs to identify parameters sets for different security strengths.

| | NIST Level Security | Level 1 | |-------------------------|-------------------------------------| | Parameters | n= 256, | | | k=2 | | | q=3329 | | | eta_1=3 | | | eta_2=2 | | | (d_u, d_v)=(10, 4) | | | delta=2^{-139} | |=========================+=====================================| | kyber-512-90s-r3 | |=========================+=====================================| | Parameter OID | {..*.. kyber-512-90s-r3} | | | <.> | | NIST Level Security | Level 1 | |-------------------------|-------------------------------------| | Parameters | n= 256, | | | k=2 | | | q=3329 | | | eta_1=3 | | | eta_2=2 | | | (d_u, d_v)=(10, 4) | | | delta=2^{-139} | |=========================+=====================================| | kyber-768-r3 | |=========================+=====================================| | Parameter OID | {..*.. kyber-768-r3} | | | <.> | | NIST Level Security | Level 3 | |-------------------------|-------------------------------------| | Parameters | n= 256, | | | k=3 | | | q=3329 | | | eta_1=2 | | | eta_2=2 | | | (d_u, d_v)=(10, 4) | | | delta=2^{-164} | |=========================+=====================================| | kyber-768-90s-r3 | |=========================+=====================================| | Parameter OID | {..*.. kyber-768-90s-r3} | | | <.> | | NIST Level Security | Level 5 | |-------------------------|-------------------------------------| | Parameters | n= 256, | | | k=3 | | | q=3329 | | | eta_1=2 | | | eta_2=2 | | | (d_u, d_v)=(10, 4) | | | delta=2^{-164} | |=========================+=====================================| | kyber-1024-r3 | |=========================+=====================================| | Parameter OID | {..*.. kyber-1024-r3} | | | <.> | | NIST Level Security | Level 5 | |-------------------------|-------------------------------------| | Parameters | n= 256, | | | k=4 | | | q=3329 | | | eta_1=2 | | | eta_2=2 | | | (d_u, d_v)=(11, 5) | | | delta=2^{-174} | |=========================+=====================================| | kyber-1024-90s-r3 | |=========================+=====================================| | Parameter OID | {..*.. kyber-1024-90s-r3} | | | <.> | | NIST Level Security | Level 5 | |-------------------------|-------------------------------------| | Parameters | n= 256, | | | k=4 | | | q=3329 | | | eta_1=2 | | | eta_2=2 | | | (d_u, d_v)=(11, 5) | | | delta=2^{-174} | |=========================+=====================================| ]]>

The '90s' variants listed above differ in the symmetric primitives that are used internally. By default, Kyber uses SHAKE-128 as XOF, SHA3 for hashing and SHAKE-256 for PRF and KDF. The '90s' variants use AES256CTR to construct a XOF and a PRF, SHA2 for hashing and SHAKE-256 as KDF. The main advantage of the '90s' variants is that they benefit from the ready availability of hardware AES and SHA2 co-processors. While the parameters listed in the table are the same, the key-pairs will not be compatible with the '90s' variants.

Key Details Public key. The public-key consists of two parameters:

• t: encoded vector A*s+e, where A is a public matrix over a constant-sized polynomial ring, s and e are vectors over the same ring.
• rho: public seed (32 bytes)

The size necessary to hold all public key elements is 12*k*n/8+32 bytes. Private key. The private key consists of 3 parameters:

• s: encoded sample from a centered binomial distribution B_{eta_1} (12*k*n/8 bytes)
• H(pk): hashed public key (32 bytes). Kyber uses SHA3-256 as H by default. The '90s' variants use SHA256 instead.
• z: a nonce (32 bytes)

If the private key is fully populated, it consists of 3 parameters. The size necessary to hold all private key elements accounts to 12*k*n/8+64 bytes, not counting the optional public key. The resulting public key and private key sizes are shown in the following table.

Private Key Full Encoding Distributing a Kyber private key with PKCS#8 requires:

• kyber-(n*k)-r3 in the algorithm field of AlgorithmIdentifier
• KyberPrivateKey in the privateKey field, which is an OCTET STRING.

When a Kyber public key is included in the distributed PrivateKeyInfo, the PublicKey field in KyberPrivateKey is used (see description of KyberPublicKey below). The ASN.1 encoding for a Kyber private key is defined as follows:

Private key Partial Encoding The partially populated parameter set uses of the fact that some parameters can be regenerated. In this case, only the initial seed 'd' (nonce) is stored and used to regenerate the full key. Partially encoded keys use the same ASN.1 structure as the fully polulated keys, simply with the regenerated fields set to EMPTY. Compared to the approach of a single definition and setting the regenratable fields as OPTIONAL, this approach significantly simplifies the processing os ASN.1 frames and validation of the partial encoding. The ASN.1 format for the partially populated versions is the same as for the fully populated version. The ASN.1 encoding for this variant (z replaced by d) is defined as follows:

Public Key Full Encoding The vector 't' is encoded using the function Encode_12, defined as the inverse of Decode_12 as defined in Algorithm 3 of the Kyber round 3 specification. The size of t is 12*k*n/8 bytes. The seed 'rho' is a 32 byte OCTET STRING.

NTRU NTRU is a key encapsulation mechanism (KEM), whose security is based on the hardness of solving the Shortest Vector Problem in NTRU lattices. Project Website: https://ntru.org/ NIST Round 3 Submission: https://csrc.nist.gov/CSRC/media/Projects/post-quantum-cryptography/documents/round-3/submissions/NTRU-Round3.zip

Algorithm Parameter Identifiers Below are the NTRU parameter sets. Note that the definition of local/non-local security is out of scope for this document, but can be found in the NTRU NIST Round 3 Submission.

| | NIST Level Security | Level 1 | |-------------------------|-------------------------------------| | Parameters | Dimension/Degree n= 509 | | | Polynomial Phin=(x^n - 1)/(x-1) | | | Polynomial Phi1=(x-1) | | | Modulus p=3 | | | Modulus q=2048 | |=========================+=====================================| | ntruhps2048677-r3 | |=========================+=====================================| | Parameter OID | {..*.. ntruhps2048677-r3} | | | <. > | | NIST Level Security | Level 3 (1) see spec. | |-------------------------|-------------------------------------| | Parameters | Dimension/Degree n=677 | | | Polynomial Phin=(x^n - 1)/(x-1) | | | Polynomial Phi1=(x-1) | | | Modulus p=3 | | | Modulus q=2048 | |=========================+=====================================| | ntruhps4096821-r3 | |=========================+=====================================| | Parameter OID | {..*.. ntruhps4096821-r3} | | | <.> | | NIST Level Security | Level 3 (1) see spec. | |-------------------------|-------------------------------------| | Parameters | Dimension/Degree n= 821 | | | Polynomial Phin=(x^n - 1)/(x-1) | | | Polynomial Phi1=(x-1) | | | Modulus p=3 | | | Modulus q= 4096 | |=========================+=====================================| | ntruhrss701-r3 | |=========================+=====================================| | Parameter OID | {..*.. ntruhrss701-r3} | | | <.> | | NIST Level Security | Level 5 (3) see spec. | |-------------------------|-------------------------------------| | Parameters | Dimension/Degree n= 701 | | | Polynomial Phin= (x^n - 1)/(x-1) | | | Polynomial Phi1=(x-1) | | | Modulus p=3 | | | Modulus q=8192 | |=========================+=====================================| ]]>

The parameter sets differ in the degree of the polynomial n and the modulus q.

Key Details Public key. The public-key consists of a single parameter :

• a polynomial h that satisfies h*f=3*g in the ring Rq=Z[x]/(q, Phi_1*Phi_n).

This means there are n - 1 coefficients of size at most q in the public key, and the size necessary to store the polynomial is therefore is ceiling((n - 1)*log2(q)/8) bytes. The resulting sizes for the parameter sets can be found in the Table below. Private key. The private key consists of 4 parameters:

• a polynomial f that is a ternary (coefficients fi are in {-1, 0, 1}) polynomial of degree n - 2, with the additional property that ∑_(i=0)^{n-3} f_i*f_{i+1}≥0,
• a polynomial f_p that satisfies f*f_p=1 in the ring Rq=Z[x]/(3, Phi_n),
• a polynomial h_q that satisfies h*h_q=1 in the ring Rq=Z[x]/(q, Phi_n), and
• a seed=fg_bits || prf_key=f_bits || g_bits || prf_key containing the randomness for the key sampling and the implicit rejection mechanism. Optionally implementers may expand this from a 32-byte seed.

This means there are 2 polynomials, f and fp, having n - 1 coefficients with absolute value at most 1 in the private key. For these polynomials, the packing algorithm in Section 1.8.7 of the Specification allows to pack 5 coefficients in a byte, so the storage requirement to store each is ceiling((n - 1)/5) bytes. Additionally hq is part of the private key, which requires the same storage size as that of the public key h, i.e. ceiling((n - 1)*log2(q)/8) bytes. For the seed bytes, the specification recommends:

• >f_bits having n - 1 bytes,
• >g_bits having n - 1 bytes for ntruhrss701, ceiling(30/8*(n-1)) bytes for the other parameter sets,
• prf_key having 32 bytes.

Implementers may choose to expand the seed from one 32-byte seed. The resulting sizes for the parameter sets can be found in the Table below. Where the seed expansion is omitted, the 32-byte seed must be replaced by key_seed_bits=sample_key_bits+prf_key_bits. The impact of these options are indicated as 32-byte seed/expanded seed in the Table below. Parameter Set Size of the public key in bytes Size of the private key in bytes

Private Key Full Encoding An NTRU private key encoded according with PKCS#8 MUST include the following two fields:

• ntruhps-(size)-r3 / ntruhrss701-r3 in the algorithm field of AlgorithmIdentifier
• NTRUPrivateKey in the privateKey field, which is an OCTET STRING.

When a NTRU public key is included in the distributed PrivateKeyInfo, the PublicKey field in NTRUPrivateKey is used (see description of NTRUPublicKey below). An NTRU private key contains f, f_p and h_q, as well as a seed. The octet string format indicates the length of the string to follow, and indicates whether the seed or expanded seed is used.

Public Key Full Encoding From the NTRU specification, the public key contains h. Each coefficient of h is encoded as an l bit sequence, where l=ceiling((n - 1)*log2(q)). Coefficients are then concatenated (two's complement, big endian convention). The final bit string is zero padded to fit into a byte sequence. NTRUPublicKey := SEQUENCE { h OCTET STRING -- integer polynomial h }

SABER SABER is a family of cryptographic primitives that rely on the hardness of the Module Learning with Rounding problem (M-LWR). Project Website: https://www.esat.kuleuven.be/cosic/pqcrypto/saber/ NIST Round 3 Submission: https://csrc.nist.gov/CSRC/media/Projects/post-quantum-cryptography/documents/round-3/submissions/SABER-Round3.zip

Algorithm Parameter Identifiers Saber has three parameter sets shown in the table below

| | NIST Level Security | Level 1 | |-------------------------|-------------------------------------| | Parameters | Degree n= 256 | | | rank of the module l=2 | | | binomial distribution with u=10 | | | Modulus q=2^{13} and p=2^{10} | |=========================+=====================================| | Saber-r3 | |=========================+=====================================| | Parameter OID | {..*.. saber-r3} | | | <.> | | NIST Level Security | Level 3 | |-------------------------|-------------------------------------| | Parameters | Degree n= 256 | | | rank of the module l=3 | | | binomial distribution with u=8 | | | Modulus q=2^{13} and p=2^{10} | |=========================+=====================================| | FireSaber-r3 | |=========================+=====================================| | Parameter OID | {..*.. firesaber-r3} | | | <.> | | NIST Level Security | Level 5 | |-------------------------|-------------------------------------| | Parameters | Degree n= 256 | | | rank of the module l=4 | | | binomial distribution with u=6 | | | Modulus q=2^{13} and p=2^{10} | |=========================+=====================================| ]]>

The rank of the module is denoted l and differs per parameter set.

Key Details Public key. The public-key consists of the following two parameters:

• >seed_A: public seed (32 bytes)
• polynomials of degree 256 with 10-bit integer coefficients denoted by vector b.

This means the size of the public key can be stored using l*256*10+256 bits. The size of the public key as used in the three parameter sets can be found in the Table below. Private key. The private key s consists of three parameters:

• a 256-bit uniform random value z
• l polynomials of degree 256 with 13-bit integer coefficients denoted by s
• H(pk): hashed public key (32 bytes)

This means the private key can be stored using 512+l*256*13 bits. The size of the private key as used in the three parameter sets can be found in the Table below.

Private Key Full Encoding A SABER private key encoded according with PKCS#8 MUST include the following two fields:

• one of the three algorithm alternatives {LightSaber-r3, Saber-r3, FireSaber-r3} in the algorithm field of AlgorithmIdentifier
• SABERPrivateKey in the privateKey field, which is an OCTET STRING.

When a SABER public key is included in the distributed PrivateKeyInfo, the PublicKey field in SABERPrivateKey is used (see the description below).

Public Key Full Encoding

CRYSTALS-DILITHIUM Dilithium is a digital signature scheme that is based on the hardness of lattice problems over module lattices. Project Website: https://pq-crystals.org/dilithium/index.shtml NIST Round 3 Submission (version 3.1): https://csrc.nist.gov/CSRC/media/Projects/post-quantum-cryptography/documents/round-3/submissions/Dilithium-Round3.zip https://pq-crystals.org/dilithium/data/dilithium-specification-round3-20210208.pdf

Algorithm Parameter Identifiers Dilithium uses OIDs to identify parameters sets for different security strengths.

| | NIST Level Security | Level 2 | |-------------------------|-------------------------------------| | Parameters | Polynomial Ring Zq[x]/( x^n+1 ) | | | Dimension/Degree n=256 | | | Modulus q=8380417 | | | Dropped bits from t: d=13 | | | # of +-1's in c: tau=39 | | | challenge entropy=192 | | | gamma coefficient range: gamma1=2^17| | | low-order rounding range: gamma2=(q-| | | 1)/88 | | | Private key Range eta=2 | | | Dimensions of A: (k,l)=(4,4) | | | Max # of 1's in the hint h: w=80 | | | Repetitions=4.25 | |=========================+=====================================| | dilithium-4x4-aes-r3 | |=========================+=====================================| | Parameter OID | {..*.. dilithium-4x4-aes-r3} | | | <.> | | NIST Level Security | Level 2 | |-------------------------|-------------------------------------| | Parameters | Polynomial Ring Zq[x]/( x^n + 1 ) | | | Dimension/Degree n=256 | | | Modulus q=8380417 | | | Dropped bits from t: d=13 | | | # of +-1's in c: tau=39 | | | challenge entropy=192 | | | y coefficient range: gamma1=2^17 | | | low-order rounding range:gamma2=(q- | | | -1)/88 | | | Private key Range eta=2 | | | Dimensions of A: (k,l)=(4,4) | | | Max # of 1's in the hint h: w=80 | | | Repetitions=4.25 | |=========================+=====================================| | dilithium-6x5-r3 | |=========================+=====================================| | Parameter OID | {..*.. dilithium-6x5-r3} | | | <.> | | NIST Level Security | Level 3 | |-------------------------|-------------------------------------| | Parameters | Polynomial Ring Zq[x]/( x^n + 1 ) | | | Dimension/Degree n=256 | | | Modulus q=8380417 | | | Dropped bits from t: d=13 | | | # of +-1's in c: tau=49 | | | challenge entropy=225 | | | y coefficient range: gamma1=2^19 | | | low-order rounding range:gamma2=(q- | | | -1)/32 | | | Private key Range eta=4 | | | Dimensions of A: (k,l)=(6,5) | | | Max # of 1's in the hint h: w=55 | | | Repetitions=5.1 | |=========================+=====================================| | dilithium-6x5-aes-r3 | |=========================+=====================================| | Parameter OID | {..*.. dilithium-6x5-aes-r3} | | | <.> | | NIST Level Security | Level 3 | |-------------------------|-------------------------------------| | Parameters | Polynomial Ring Zq[x]/( x^n +1 ) | | | Dimension/Degree n=256 | | | Modulus q=8380417 | | | Dropped bits from t: d=13 | | | # of +-1's in c: tau=49 | | | challenge entropy=225 | | | y coefficient range: gamma1=2^19 | | | low-order rounding range:gamma2=(q- | | | -1)/32 | | | Private key Range eta=4 | | | Dimensions of A: (k,l)=(6,5) | | | Max # of 1's in the hint h: w=55 | | | Repetitions=5.1 | |=========================+=====================================| | dilithium-8x7-r3 | |=========================+=====================================| | Parameter OID | {..*.. dilithium-8x7-r3} | | | <.> | | NIST Level Security | Level 5 | |-------------------------|-------------------------------------| | Parameters | Polynomial Ring Zq[x]/( x^n + 1 ) | | | Dimension/Degree n=256 | | | Modulus q=8380417 | | | Dropped bits from t: d=13 | | | # of +-1's in c: tau=60 | | | challenge entropy=257 | | | y coefficient range: gamma1=2^19 | | | low-order rounding range:gamma2=(q- | | | -1)/32 | | | Private key Range eta=2 | | | Dimensions of A: (k,l)=(8,7) | | | Max # of 1's in the hint h: w=75 | | | Repetitions=3.85 | |=========================+=====================================| | dilithium-8x7-aes-r3 | |=========================+=====================================| | Parameter OID | {..*.. dilithium-8x7-aes-r3} | | | <.> | | NIST Level Security | Level 5 | |-------------------------|-------------------------------------| | Parameters | Polynomial Ring Zq[x]/( x^n + 1 ) | | | Dimension/Degree n=256 | | | Modulus q=8380417 | | | Dropped bits from t: d=13 | | | # of +-1's in c: tau=60 | | | challenge entropy=257 | | | y coefficient range: gamma1=2^19 | | | low-order rounding range:gamma2=(q- | | | -1)/32 | | | Private key Range eta=2 | | | Dimensions of A: (k,l)=(8,7) | | | Max # of 1's in the hint h: w=75 | | | Repetitions=3.85 | |=========================+=====================================| ]]>

The aes variants listed above differ from the other variants in that they use AES, rather than SHAKE internally to expand the key parameters from an initial seed. While the parameters listed in the table are the same, the key-pairs will not be compatible with the 'aes' variants.

Key Details Public key. The public-key consists of two parameters:

• rho: nonce
• t1: a vector encoded in 320*k bytes

The size necessary to hold all public key elements accounts to 32+320*k bytes. Private key. The private key consists of 6 parameters:

• rho: nonce
• K: a key/seed/D
• tr: PRF bytes
• s1: vector (L)
• s2: vector (K)
• t0: k polynomials

If the private key is fully populated, it consists of 6 parameters. The size necessary to hold all private key elements accounts to 32+32+32+32*[(k+l)*ceiling(log(2*eta+1))+13*k] bytes. The resulting public key and private key sizes can be found in the table below.

Private Key Full Encoding A Dilithium private key encoded according with PKCS#8 MUST include the following two fields:

• dilithium-(kxl)-r3 in the algorithm field of AlgorithmIdentifier
• DilithiumPrivateKey in the privateKey field, which is an OCTET STRING.

Dilithium public key are optionally distributed in the PublicKey field of the PrivateKeyInfo structure. ASN.1 Encoding for a Dilithium private key for fully populated:

Private key Partial Encoding Option 1 In option 1 of Dilithium partial encoding the rho (nonce) and the seed (key) are used to regenerate the full key. Note: There are a number of alternative ways to encode a partially filled structure that include defining fields as optional and defining fields as 'EMPTY'. As an example partial RSA keys are encoded using EMPTY fields. It can be argued that defining fields as EMPTY significantly simplifies the implementation of parsing ASN.1 frames. The ASN.1 format for the partially populated versions is the same as for the fully populated version. The ASN.1 encoding for the first variant (rho and seed) is defined as follows:

Private key Partial Encoding Option 2 In option 2 of Dilithium partial encoding only zeta (nonce) is used to regenerate the full key. The ASN.1 encoding for this is defined as follows:

Public Key Full Encoding Components are individual OCTET STRINGs, without unused bits, encoded with the exact size. There is no removal of leading zeroes.

FALCON FALCON is a lattice-based signature scheme that uses the short integer solution problem (SIS) over NTRU lattices as its underlying hard problem. Project Website https://falcon-sign.info/ NIST Round 3 Submission https://csrc.nist.gov/CSRC/media/Projects/post-quantum-cryptography/documents/round-3/submissions/Falcon-Round3.zip

Algorithm Parameter Identifiers

| | NIST Level Security | Level 1 | |-------------------------|-------------------------------------| | Parameters | Dimension/Degree n = 512 | | | Polynomial Phi = 1+x^n | | | Modulus q = 12289 | | | Max. signature square norm | | | floor (beta^2) = 34034726 | | | Standard deviation = 165.736617183 | | | sigma_{max} = 1.8205 | | | sigma_{min} = 1.27783369 | |=========================+=====================================| | falcon1024-r3 | |=========================+=====================================| | Parameter OID | {..*.. falcon1024-r3} | | | <.> | | NIST Level Security | Level 5 | |-------------------------|-------------------------------------| | Parameters | Dimension/Degree n = 1024 | | | Polynomial Phi = 1+x^n | | | Modulus q = 12289 | | | Max. signature square norm | | | floor (beta^2) = 34034726 | | | Standard deviation = 168.388571447 | | | sigma_{max} = 1.8205 | | | sigma_{min} = 1.298280334 | |=========================+=====================================| ]]>

Key Details The FALCON private key contains the key components f, g and F. Each coefficient of f and g is encoded over a fixed number of bits, which depends on the degree of f and g: 6 bits each for degree 512 (parameter name = falcon512-r3) and 5 bits each for degree 1024 (parameter name = falcon1024-r3). Coefficients of F use 8 bits each, regardless of its degree. Each coefficient uses signed encoding, with two's complement for negative values. Moreover, the minimal value is forbidden, e.g. when using degree 512, the valid range for a coefficient of f or g is -31 to +31; -32 is not allowed.

Private Key Full Encoding Encoding a FALCON private key with PKCS#8 must include the following two fields:

• falcon-(degree)-r3 in the algorithm field of AlgorithmIdentifier
• FALCONPrivateKey in the privateKey field, which is an OCTET STRING.

When a FALCON public key is included in the distributed PrivateKeyInfo, the PublicKey field in FALCONPrivateKey is used (see description of FALCONPublicKey below). ASN.1 Encoding for a FALCON private key:

Public Key Full Encoding The FALCON public key contains a series of coefficients encoded into parameter h. Each coefficient of h is encoded as a 14 bit sequence (since q = 12289, 14 bits per coefficient are used). Coefficients are then concatenated. The final bit string is zero padded to fit into a byte sequence.

Rainbow Rainbow is a multivariate-based signature scheme that relies on the hardness of solving a set of random multivariate quadratic systems. Project Website: https://www.pqcrainbow.org/ NIST Round Submission: https://csrc.nist.gov/CSRC/media/Projects/post-quantum-cryptography/documents/round-3/submissions/Rainbow-Round3.zip

Algorithm Parameter Identifiers The following tables shows Rainbow parameter sets.

| | NIST Level Security | Level 1 / Level 2 see spec. | |-------------------------|-------------------------------------| | Parameters | Field F = GF(16)[2] | | | u = 2 | | | v1 = 36 | | | o1 = 32 | | | o2 = 32 | | | n = v2 = 100[3] | | | m = n - v1 = 64 | |=========================+=====================================| | rainbowIII-r3 | |=========================+=====================================| | Parameter OID | {..*.. rainbowIII-r3 | | | <.> | | NIST Level Security | Level 3 / Level 4. See spec. | |-------------------------|-------------------------------------| | Parameters | Field F = GF(256) | | | u = 2 | | | v1 = 68 | | | o1 = 32 | | | o2 = 48 | | | n = v2 = 148 | | | m = n - v1 = 80 | |=========================+=====================================| | rainbowV-r3 | |=========================+=====================================| | Parameter OID | {..*.. rainbowV-r3} | | | <.> | | NIST Level Security | Level 5 | |-------------------------|-------------------------------------| | Parameters | Field F = GF(256) | | | u = 2 | | | v1 = 96 | | | o1 = 36 | | | o2 = 64 | | | n = v2 = 196 | | | m = n - v1 = 100 | |=========================+=====================================| ]]>

Key Details Public key. The public-key consists of two parameters:

• P: a mapping from F^{n} to F^{m}
• ell: length of the used salt. Needs to be included to reach EUF- CMA security.

This mapping can be expressed as m quadratic polynomials in the ring F[x1, … , xn], which means the public key consists of m*(n+1)*(n+2)/2 elements of F. With optimizations (see Rainbow specification), this can be reduced to m*n*(n+1)/2 elements of F. The size necessary to hold all public key elements accounts to m*n*(n+1)/16*f bytes, where f=4 for rainbowI and 8 for rainbowIII and rainbowV. For all parameter sets ell is 16 bytes. Private key. The private key consists of 4 parameters:

• S: affine map from F^{m} to F^{m}
• T: affine map from F^{n} to F^{n}
• F: quadratic central map of F^{n} to F^{n}
• ell: length of the used salt. Needs to be included to reach EUF- CMA security.

The affine mappings S and T can respectively be expressed in terms of m*(m+1) and n*(n+1) elements of F. The central map F mapping can be expressed as m multivariate polynomials and be stored as o1*(v1*(v1+1)/2 + v1*o1)+ o2*((v1+ o1)*(v1+o1+1)/2 +(v1+o1)*o2) field elements (see section 4.1 of the Rainbow specification). Rainbow can be instantiated in its CZ-Rainbow form. The key generation method is then inverted. This allows parts of the public key to be fixed and therefore reproduced from a partially stored public key. Public key - CZ. The public-key of CZ-Rainbow consists of 3 parameters:

• 256-bit seed spub
• P: a partially stored mapping from Fn to Fm
• ell: length of the used salt. Needs to be included to reach EUF- CMA security

The partial public key now consists of 5 submatrices totaling o1*o2*v1 + o1*o1*(o1+1)/2 +o1*o2*o1 + o1*o2*(o2+1)/2 + o2*o2*(o2+1)/2 elements of F. Additionally the seed spub is 32 bytes. The private key can also be stored as the seeds of the key generation process spriv (32 bytes) and spub (32 bytes). This is denoted as the compressed key and has a size of total 64 bytes. The resulting public key and private key sizes can be found in the table below.

Private Key Full Encoding A Rainbow private key encoded according with PKCS#8 MUST include the following two fields:

• rainbow-{eclvl}-r3 in the algorithm field of AlgorithmIdentifier
• RainbowPrivateKey in the privateKey field, which is an OCTET STRING.

When a Rainbow public key is included in the distributed PrivateKeyInfo, the PublicKey field in RainbowPrivateKey is used (see description of RainbowPublicKey below). ASN.1 Encoding for a fully populated rainbow private key:

Private key Partial Encoding A partially populated private key is used when Compressed Rainbow is used. In this case, spriv and spub are used to regenerate the full key. The ASN.1 encoding is then defined as follows:

Public Key Full Encoding Public keys can either be distributed stand-alone as subjectPublicKeyInfo or optionally be included in PrivateKeyInfo (::=OneAsymmetricKey) and distributed together with the corresponding private key. Once the RainbowPublicKey below is encoded as OCTET STRING (subjectPublicKey in subjectPublicKeyInfo) and once as BIT STRING (publicKey in OneAsymmetricKey). The public key for the standard Rainbow scheme consists of an EMPTY spub field, and P consists of encoding of respectively GF(16) and GF(256) field elements appended to form OCTET STRINGS. The CZ variant of rainbow then includes a 32-byte seed spub, which reduces the number of field elements encoded in P.

Acknowledgements This template was derived from an initial version written by Pekka Savola and contributed by him to the xml2rfc project. This document is part of a plan to make xml2rfc indispensable.

IANA Considerations This memo includes no request to IANA.

Security Considerations Any processing of the ASN.1 private key structures, such as base64 en/decoding shall be performed in "constant-time", meaning without secret-dependent control flow and table lookups. The ASN.1 structures in this document are defined with fixed tag-lengths. The purpose is to prevent side-channel leakage of variable lengths during DER parsing. Any DER parsing of the private key ASN.1 key structures shall be performed with these fixed lengths.

References Normative References In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. Informative References This memo presents a technique for using XML (Extensible Markup Language) as a source format for documents in the Internet-Drafts (I-Ds) and Request for Comments (RFC) series. This memo provides information for the Internet community. All RFCs are required to have a Security Considerations section. Historically, such sections have been relatively weak. This document provides guidelines to RFC authors on how to write a good Security Considerations section. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. This RFC addresses key identification, key serialization, and key compression for the set of quantum safe algorithms currently under evaluation in the NIST PQC process. The aim of this RFC is to facilitate the management of key material as these algorithms evolve through standardization phases into production. Early definition of key material is expected to expedite the adoption of new quantum safe algorithms at the same time as improving interoperability and preventing diverging standards.

Additional Stuff This becomes an Appendix.