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derived_reader.go
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/
derived_reader.go
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package crypto
import (
"context"
"crypto/sha256"
"fmt"
"io"
wrapping "github.com/hxfs/go-kms-wrapping/v2"
"golang.org/x/crypto/hkdf"
)
// DerivedReader returns a reader from which keys can be read, using the
// given wrapper, reader length limit, salt and context info. Salt and info can
// be nil.
//
// Example:
// reader, _ := crypto.NewDerivedReader(wrapper, userId, jobId)
// key := ed25519.GenerateKey(reader)
func NewDerivedReader(ctx context.Context, wrapper wrapping.Wrapper, lenLimit int64, opt ...wrapping.Option) (*io.LimitedReader, error) {
const (
op = "reader.NewDerivedReader"
minLen = 20
)
if wrapper == nil {
return nil, fmt.Errorf("%s: missing wrapper: %w", op, wrapping.ErrInvalidParameter)
}
if lenLimit < minLen {
return nil, fmt.Errorf("%s: lenLimit must be >= %d: %w", op, minLen, wrapping.ErrInvalidParameter)
}
biter, ok := wrapper.(wrapping.KeyExporter)
if !ok {
return nil, fmt.Errorf("%s: wrapper does not implement required KeyBytes interface: %w", op, wrapping.ErrInvalidParameter)
}
b, err := biter.KeyBytes(ctx)
if err != nil {
return nil, fmt.Errorf("%s: unable to get current key bytes: %w", op, err)
}
if b == nil {
return nil, fmt.Errorf("%s: wrapper missing bytes: %w", op, wrapping.ErrInvalidParameter)
}
opts, err := getOpts(opt...)
if err != nil {
return nil, fmt.Errorf("%s: unable to get options %w", op, err)
}
reader := hkdf.New(sha256.New, b, opts.withSalt, opts.withInfo)
return &io.LimitedReader{
R: reader,
N: lenLimit,
}, nil
}