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good_key.go
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good_key.go
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// Copyright 2014 ISRG. All rights reserved
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at http://mozilla.org/MPL/2.0/.
package core
import (
"crypto"
"crypto/ecdsa"
"crypto/rsa"
"fmt"
blog "github.com/letsencrypt/boulder/log"
"math/big"
"reflect"
"sync"
)
// To generate, run: primes 2 752 | tr '\n' ,
var smallPrimeInts = []int64{
2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47,
53, 59, 61, 67, 71, 73, 79, 83, 89, 97, 101, 103, 107,
109, 113, 127, 131, 137, 139, 149, 151, 157, 163, 167,
173, 179, 181, 191, 193, 197, 199, 211, 223, 227, 229,
233, 239, 241, 251, 257, 263, 269, 271, 277, 281, 283,
293, 307, 311, 313, 317, 331, 337, 347, 349, 353, 359,
367, 373, 379, 383, 389, 397, 401, 409, 419, 421, 431,
433, 439, 443, 449, 457, 461, 463, 467, 479, 487, 491,
499, 503, 509, 521, 523, 541, 547, 557, 563, 569, 571,
577, 587, 593, 599, 601, 607, 613, 617, 619, 631, 641,
643, 647, 653, 659, 661, 673, 677, 683, 691, 701, 709,
719, 727, 733, 739, 743, 751,
}
// singleton defines the object of a Singleton pattern
var (
smallPrimesSingleton sync.Once
smallPrimes []*big.Int
)
// GoodKey returns true iff the key is acceptable for both TLS use and account
// key use (our requirements are the same for either one), according to basic
// strength and algorithm checking.
// TODO: Support JsonWebKeys once go-jose migration is done.
func GoodKey(key crypto.PublicKey) error {
log := blog.GetAuditLogger()
switch t := key.(type) {
case rsa.PublicKey:
return GoodKeyRSA(t)
case *rsa.PublicKey:
return GoodKeyRSA(*t)
case ecdsa.PublicKey:
return GoodKeyECDSA(t)
case *ecdsa.PublicKey:
return GoodKeyECDSA(*t)
default:
err := MalformedRequestError(fmt.Sprintf("Unknown key type %s", reflect.TypeOf(key)))
log.Debug(err.Error())
return err
}
}
// GoodKeyECDSA determines if an ECDSA pubkey meets our requirements
func GoodKeyECDSA(key ecdsa.PublicKey) (err error) {
log := blog.GetAuditLogger()
err = NotSupportedError("ECDSA keys not yet supported")
log.Debug(err.Error())
return
}
// GoodKeyRSA determines if a RSA pubkey meets our requirements
func GoodKeyRSA(key rsa.PublicKey) (err error) {
log := blog.GetAuditLogger()
// Baseline Requirements Appendix A
// Modulus must be >= 2048 bits and <= 4096 bits
modulus := key.N
modulusBitLen := modulus.BitLen()
const maxKeySize = 4096
if modulusBitLen < 2048 {
err = MalformedRequestError(fmt.Sprintf("Key too small: %d", modulusBitLen))
log.Debug(err.Error())
return err
}
if modulusBitLen > maxKeySize {
err = MalformedRequestError(fmt.Sprintf("Key too large: %d > %d", modulusBitLen, maxKeySize))
log.Debug(err.Error())
return err
}
// The CA SHALL confirm that the value of the public exponent is an
// odd number equal to 3 or more. Additionally, the public exponent
// SHOULD be in the range between 2^16 + 1 and 2^256-1.
// NOTE: rsa.PublicKey cannot represent an exponent part greater than
// 2^32 - 1 or 2^64 - 1, because it stores E as an integer. So we
// don't need to check the upper bound.
if (key.E%2) == 0 || key.E < ((1<<16)+1) {
err = MalformedRequestError(fmt.Sprintf("Key exponent should be odd and >2^16: %d", key.E))
log.Debug(err.Error())
return err
}
// The modulus SHOULD also have the following characteristics: an odd
// number, not the power of a prime, and have no factors smaller than 752.
// TODO: We don't yet check for "power of a prime."
smallPrimesSingleton.Do(func() {
for _, prime := range smallPrimeInts {
smallPrimes = append(smallPrimes, big.NewInt(prime))
}
})
for _, prime := range smallPrimes {
var result big.Int
result.Mod(modulus, prime)
if result.Sign() == 0 {
err = MalformedRequestError(fmt.Sprintf("Key divisible by small prime: %d", prime))
log.Debug(err.Error())
return err
}
}
return nil
}