Struct ring::signature::RsaKeyPair

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pub struct RsaKeyPair { /* private fields */ }

Expand description

An RSA key pair, used for signing.

Implementations

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impl RsaKeyPair

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pub fn from_pkcs8(pkcs8: &[u8]) -> Result<Self, KeyRejected>

Parses an unencrypted PKCS#8-encoded RSA private key.

Only two-prime (not multi-prime) keys are supported. The public modulus (n) must be at least 2047 bits. The public modulus must be no larger than 4096 bits. It is recommended that the public modulus be exactly 2048 or 3072 bits. The public exponent must be at least 65537.

This will generate a 2048-bit RSA private key of the correct form using OpenSSL’s command line tool:

   openssl genpkey -algorithm RSA \
       -pkeyopt rsa_keygen_bits:2048 \
       -pkeyopt rsa_keygen_pubexp:65537 | \
     openssl pkcs8 -topk8 -nocrypt -outform der > rsa-2048-private-key.pk8

This will generate a 3072-bit RSA private key of the correct form:

   openssl genpkey -algorithm RSA \
       -pkeyopt rsa_keygen_bits:3072 \
       -pkeyopt rsa_keygen_pubexp:65537 | \
     openssl pkcs8 -topk8 -nocrypt -outform der > rsa-3072-private-key.pk8

Often, keys generated for use in OpenSSL-based software are stored in the Base64 “PEM” format without the PKCS#8 wrapper. Such keys can be converted to binary PKCS#8 form using the OpenSSL command line tool like this:

openssl pkcs8 -topk8 -nocrypt -outform der \
    -in rsa-2048-private-key.pem > rsa-2048-private-key.pk8

Base64 (“PEM”) PKCS#8-encoded keys can be converted to the binary PKCS#8 form like this:

openssl pkcs8 -nocrypt -outform der \
    -in rsa-2048-private-key.pem > rsa-2048-private-key.pk8

The private key is validated according to NIST SP-800-56B rev. 1 section 6.4.1.4.3, crt_pkv (Intended Exponent-Creation Method Unknown), with the following exceptions:

Section 6.4.1.2.1, Step 1: Neither a target security level nor an expected modulus length is provided as a parameter, so checks regarding these expectations are not done.
Section 6.4.1.2.1, Step 3: Since neither the public key nor the expected modulus length is provided as a parameter, the consistency check between these values and the private key’s value of n isn’t done.
Section 6.4.1.2.1, Step 5: No primality tests are done, both for performance reasons and to avoid any side channels that such tests would provide.
Section 6.4.1.2.1, Step 6, and 6.4.1.4.3, Step 7:
- ring has a slightly looser lower bound for the values of p and q than what the NIST document specifies. This looser lower bound matches what most other crypto libraries do. The check might be tightened to meet NIST’s requirements in the future. Similarly, the check that p and q are not too close together is skipped currently, but may be added in the future.
- The validity of the mathematical relationship of dP, dQ, e and n is verified only during signing. Some size checks of d, dP and dQ are performed at construction, but some NIST checks are skipped because they would be expensive and/or they would leak information through side channels. If a preemptive check of the consistency of dP, dQ, e and n with each other is necessary, that can be done by signing any message with the key pair.
- d is not fully validated, neither at construction nor during signing. This is OK as far as ring’s usage of the key is concerned because ring never uses the value of d (ring always uses p, q, dP and dQ via the Chinese Remainder Theorem, instead). However, ring’s checks would not be sufficient for validating a key pair for use by some other system; that other system must check the value of d itself if d is to be used.

In addition to the NIST requirements, ring requires that p > q and that e must be no more than 33 bits.

See RFC 5958 and RFC 3447 Appendix A.1.2 for more details of the encoding of the key.

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pub fn from_der(input: &[u8]) -> Result<Self, KeyRejected>

Parses an RSA private key that is not inside a PKCS#8 wrapper.

The private key must be encoded as a binary DER-encoded ASN.1 RSAPrivateKey as described in RFC 3447 Appendix A.1.2). In all other respects, this is just like from_pkcs8(). See the documentation for from_pkcs8() for more details.

It is recommended to use from_pkcs8() (with a PKCS#8-encoded key) instead.

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pub fn public_modulus_len(&self) -> usize

Returns the length in bytes of the key pair’s public modulus.

A signature has the same length as the public modulus.

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impl RsaKeyPair

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pub fn sign(
 &self,
 padding_alg: &'static dyn RsaEncoding,
 rng: &dyn SecureRandom,
 msg: &[u8],
 signature: &mut [u8]
) -> Result<(), Unspecified>

Sign msg. msg is digested using the digest algorithm from padding_alg and the digest is then padded using the padding algorithm from padding_alg. The signature it written into signature; signature’s length must be exactly the length returned by public_modulus_len(). rng may be used to randomize the padding (e.g. for PSS).

Many other crypto libraries have signing functions that takes a precomputed digest as input, instead of the message to digest. This function does not take a precomputed digest; instead, sign calculates the digest itself.

Lots of effort has been made to make the signing operations close to constant time to protect the private key from side channel attacks. On x86-64, this is done pretty well, but not perfectly. On other platforms, it is done less perfectly.