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package s2k
import "crypto"
// Config collects configuration parameters for s2k key-stretching
// transformations. A nil *Config is valid and results in all default
// values.
type Config struct {
// S2K (String to Key) mode, used for key derivation in the context of secret key encryption
// and passphrase-encrypted data. Either s2k.Argon2S2K or s2k.IteratedSaltedS2K may be used.
// If the passphrase is a high-entropy key, indicated by setting PassphraseIsHighEntropy to true,
// s2k.SaltedS2K can also be used.
// Note: Argon2 is the strongest option but not all OpenPGP implementations are compatible with it
//(pending standardisation).
// 0 (simple), 1(salted), 3(iterated), 4(argon2)
// 2(reserved) 100-110(private/experimental).
S2KMode Mode
// Only relevant if S2KMode is not set to s2k.Argon2S2K.
// Hash is the default hash function to be used. If
// nil, SHA256 is used.
Hash crypto.Hash
// Argon2 parameters for S2K (String to Key).
// Only relevant if S2KMode is set to s2k.Argon2S2K.
// If nil, default parameters are used.
// For more details on the choice of parameters, see https://tools.ietf.org/html/rfc9106#section-4.
Argon2Config *Argon2Config
// Only relevant if S2KMode is set to s2k.IteratedSaltedS2K.
// Iteration count for Iterated S2K (String to Key). It
// determines the strength of the passphrase stretching when
// the said passphrase is hashed to produce a key. S2KCount
// should be between 65536 and 65011712, inclusive. If Config
// is nil or S2KCount is 0, the value 16777216 used. Not all
// values in the above range can be represented. S2KCount will
// be rounded up to the next representable value if it cannot
// be encoded exactly. When set, it is strongly encrouraged to
// use a value that is at least 65536. See RFC 4880 Section
// 3.7.1.3.
S2KCount int
// Indicates whether the passphrase passed by the application is a
// high-entropy key (e.g. it's randomly generated or derived from
// another passphrase using a strong key derivation function).
// When true, allows the S2KMode to be s2k.SaltedS2K.
// When the passphrase is not a high-entropy key, using SaltedS2K is
// insecure, and not allowed by draft-ietf-openpgp-crypto-refresh-08.
PassphraseIsHighEntropy bool
}
// Argon2Config stores the Argon2 parameters
// A nil *Argon2Config is valid and results in all default
type Argon2Config struct {
NumberOfPasses uint8
DegreeOfParallelism uint8
// Memory specifies the desired Argon2 memory usage in kibibytes.
// For example memory=64*1024 sets the memory cost to ~64 MB.
Memory uint32
}
func (c *Config) Mode() Mode {
if c == nil {
return IteratedSaltedS2K
}
return c.S2KMode
}
func (c *Config) hash() crypto.Hash {
if c == nil || uint(c.Hash) == 0 {
return crypto.SHA256
}
return c.Hash
}
func (c *Config) Argon2() *Argon2Config {
if c == nil || c.Argon2Config == nil {
return nil
}
return c.Argon2Config
}
// EncodedCount get encoded count
func (c *Config) EncodedCount() uint8 {
if c == nil || c.S2KCount == 0 {
return 224 // The common case. Corresponding to 16777216
}
i := c.S2KCount
switch {
case i < 65536:
i = 65536
case i > 65011712:
i = 65011712
}
return encodeCount(i)
}
func (c *Argon2Config) Passes() uint8 {
if c == nil || c.NumberOfPasses == 0 {
return 3
}
return c.NumberOfPasses
}
func (c *Argon2Config) Parallelism() uint8 {
if c == nil || c.DegreeOfParallelism == 0 {
return 4
}
return c.DegreeOfParallelism
}
func (c *Argon2Config) EncodedMemory() uint8 {
if c == nil || c.Memory == 0 {
return 16 // 64 MiB of RAM
}
memory := c.Memory
lowerBound := uint32(c.Parallelism()) * 8
upperBound := uint32(2147483648)
switch {
case memory < lowerBound:
memory = lowerBound
case memory > upperBound:
memory = upperBound
}
return encodeMemory(memory, c.Parallelism())
}
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