Package com.google.crypto.tink.internal

Class EllipticCurvesUtil

  • public final class EllipticCurvesUtil
extends java.lang.Object
    Utility functions for elliptic curve crypto, used in ECDSA and ECDH.

    • Field Summary

      Fields 
      Modifier and Type Field Description
      static java.security.spec.ECParameterSpec NIST_P256_PARAMS  
      static java.security.spec.ECParameterSpec NIST_P384_PARAMS  
      static java.security.spec.ECParameterSpec NIST_P521_PARAMS  

    • Method Summary

      All Methods Static Methods Concrete Methods 
      Modifier and Type Method Description
      static void checkPointOnCurve​(java.security.spec.ECPoint point, java.security.spec.EllipticCurve ec)
      Checks that a point is on a given elliptic curve.
      static java.math.BigInteger getModulus​(java.security.spec.EllipticCurve curve)
      Returns the modulus of the field used by the curve specified in ecParams.
      static boolean isNistEcParameterSpec​(java.security.spec.ECParameterSpec spec)
      Returns whether spec is a ECParameterSpec of one of the NIST curves.
      static boolean isSameEcParameterSpec​(java.security.spec.ECParameterSpec one, java.security.spec.ECParameterSpec two)
      Returns whether one is the same ECParameterSpec as two.
      static java.security.spec.ECPoint multiplyByGenerator​(java.math.BigInteger x, java.security.spec.ECParameterSpec spec)
      Calculates x times the generator of the give elliptic curve spec using the Montgomery ladder.

      • Methods inherited from class java.lang.Object

        clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

    • Field Detail

      • NIST_P256_PARAMS

        public static final java.security.spec.ECParameterSpec NIST_P256_PARAMS

      • NIST_P384_PARAMS

        public static final java.security.spec.ECParameterSpec NIST_P384_PARAMS

      • NIST_P521_PARAMS

        public static final java.security.spec.ECParameterSpec NIST_P521_PARAMS

    • Method Detail

      • checkPointOnCurve

        public static void checkPointOnCurve​(java.security.spec.ECPoint point,
                                     java.security.spec.EllipticCurve ec)
                              throws java.security.GeneralSecurityException
        Checks that a point is on a given elliptic curve.

        This method implements the partial public key validation routine from Section 5.6.2.6 of NIST SP 800-56A. A partial public key validation is sufficient for curves with cofactor 1. See Section B.3 of http://www.nsa.gov/ia/_files/SuiteB_Implementer_G-113808.pdf.

        The point validations above are taken from recommendations for ECDH, because parameter checks in ECDH are much more important than for the case of ECDSA. Performing this test for ECDSA keys is mainly a sanity check.

        Parameters:
        point - the point that needs verification
        ec - the elliptic curve. This must be a curve over a prime order field.
        Throws:
        java.security.GeneralSecurityException - if the field is binary or if the point is not on the curve.

      • isNistEcParameterSpec

        public static boolean isNistEcParameterSpec​(java.security.spec.ECParameterSpec spec)
        Returns whether spec is a ECParameterSpec of one of the NIST curves.

      • isSameEcParameterSpec

        public static boolean isSameEcParameterSpec​(java.security.spec.ECParameterSpec one,
                                            java.security.spec.ECParameterSpec two)
        Returns whether one is the same ECParameterSpec as two.

      • getModulus

        public static java.math.BigInteger getModulus​(java.security.spec.EllipticCurve curve)
                                       throws java.security.GeneralSecurityException
        Returns the modulus of the field used by the curve specified in ecParams.
        Parameters:
        curve - must be a prime order elliptic curve
        Returns:
        the order of the finite field over which curve is defined.
        Throws:
        java.security.GeneralSecurityException

      • multiplyByGenerator

        public static java.security.spec.ECPoint multiplyByGenerator​(java.math.BigInteger x,
                                                             java.security.spec.ECParameterSpec spec)
                                                      throws java.security.GeneralSecurityException
        Calculates x times the generator of the give elliptic curve spec using the Montgomery ladder.

        This should only be used to validate keys, and not to sign or verify messages.

        See: Elliptic curve point multiplication.

        Parameters:
        x - must be larger than 0 and smaller than the order of the generator.
        Returns:
        the ECPoint that is x times the generator.
        Throws:
        java.security.GeneralSecurityException