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-rw-r--r--crypto/srp/srp_vfy.c101
1 files changed, 95 insertions, 6 deletions
diff --git a/crypto/srp/srp_vfy.c b/crypto/srp/srp_vfy.c
index 1eba5a7cb1..1bf2f267ed 100644
--- a/crypto/srp/srp_vfy.c
+++ b/crypto/srp/srp_vfy.c
@@ -26,6 +26,15 @@
# define MAX_LEN 2500
/*
+ * Note that SRP uses its own variant of base 64 encoding. A different base64
+ * alphabet is used and no padding '=' characters are added. Instead we pad to
+ * the front with 0 bytes and subsequently strip off leading encoded padding.
+ * This variant is used for compatibility with other SRP implementations -
+ * notably libsrp, but also others. It is also required for backwards
+ * compatibility in order to load verifier files from other OpenSSL versions.
+ */
+
+/*
* Convert a base64 string into raw byte array representation.
* Returns the length of the decoded data, or -1 on error.
*/
@@ -33,24 +42,79 @@ static int t_fromb64(unsigned char *a, size_t alen, const char *src)
{
EVP_ENCODE_CTX *ctx;
int outl = 0, outl2 = 0;
- size_t size = strlen(src);
+ size_t size, padsize;
+ const unsigned char *pad = (const unsigned char *)"00";
- if (size > INT_MAX)
+ while (*src == ' ' || *src == '\t' || *src == '\n')
+ ++src;
+ size = strlen(src);
+ padsize = 4 - (size & 3);
+ padsize &= 3;
+
+ /* Four bytes in src become three bytes output. */
+ if (size > INT_MAX || ((size + padsize) / 4) * 3 > alen)
return -1;
ctx = EVP_ENCODE_CTX_new();
if (ctx == NULL)
return -1;
+ /*
+ * This should never occur because 1 byte of data always requires 2 bytes of
+ * encoding, i.e.
+ * 0 bytes unencoded = 0 bytes encoded
+ * 1 byte unencoded = 2 bytes encoded
+ * 2 bytes unencoded = 3 bytes encoded
+ * 3 bytes unencoded = 4 bytes encoded
+ * 4 bytes unencoded = 6 bytes encoded
+ * etc
+ */
+ if (padsize == 3)
+ return -1;
+
+ /* Valid padsize values are now 0, 1 or 2 */
+
EVP_DecodeInit(ctx);
- if (EVP_DecodeUpdate(ctx, a, &outl, (const unsigned char *)src, size) < 0) {
+ evp_encode_ctx_set_flags(ctx, EVP_ENCODE_CTX_USE_SRP_ALPHABET);
+
+ /* Add any encoded padding that is required */
+ if (padsize != 0
+ && EVP_DecodeUpdate(ctx, a, &outl, pad, padsize) < 0) {
EVP_ENCODE_CTX_free(ctx);
return -1;
}
+ if (EVP_DecodeUpdate(ctx, a, &outl2, (const unsigned char *)src, size) < 0) {
+ EVP_ENCODE_CTX_free(ctx);
+ return -1;
+ }
+ outl += outl2;
EVP_DecodeFinal(ctx, a + outl, &outl2);
+ outl += outl2;
+
+ /* Strip off the leading padding */
+ if (padsize != 0) {
+ if ((int)padsize >= outl)
+ return -1;
+ /*
+ * If we added 1 byte of padding prior to encoding then we have 2 bytes
+ * of "real" data which gets spread across 4 encoded bytes like this:
+ * (6 bits pad)(2 bits pad | 4 bits data)(6 bits data)(6 bits data)
+ * So 1 byte of pre-encoding padding results in 1 full byte of encoded
+ * padding.
+ * If we added 2 bytes of padding prior to encoding this gets encoded
+ * as:
+ * (6 bits pad)(6 bits pad)(4 bits pad | 2 bits data)(6 bits data)
+ * So 2 bytes of pre-encoding padding results in 2 full bytes of encoded
+ * padding, i.e. we have to strip the same number of bytes of padding
+ * from the encoded data as we added to the pre-encoded data.
+ */
+ memmove(a, a + padsize, outl - padsize);
+ outl -= padsize;
+ }
EVP_ENCODE_CTX_free(ctx);
- return outl + outl2;
+
+ return outl;
}
/*
@@ -61,18 +125,43 @@ static int t_tob64(char *dst, const unsigned char *src, int size)
{
EVP_ENCODE_CTX *ctx = EVP_ENCODE_CTX_new();
int outl = 0, outl2 = 0;
+ unsigned char pad[2] = {0, 0};
+ size_t leadz = 0;
if (ctx == NULL)
return 0;
EVP_EncodeInit(ctx);
- evp_encode_ctx_set_flags(ctx, EVP_ENCODE_CTX_NO_NEWLINES);
+ evp_encode_ctx_set_flags(ctx, EVP_ENCODE_CTX_NO_NEWLINES
+ | EVP_ENCODE_CTX_USE_SRP_ALPHABET);
- if (!EVP_EncodeUpdate(ctx, (unsigned char *)dst, &outl, src, size)) {
+ /*
+ * We pad at the front with zero bytes until the length is a multiple of 3
+ * so that EVP_EncodeUpdate/EVP_EncodeFinal does not add any of its own "="
+ * padding
+ */
+ leadz = 3 - (size % 3);
+ if (leadz != 3
+ && !EVP_EncodeUpdate(ctx, (unsigned char *)dst, &outl, pad,
+ leadz)) {
EVP_ENCODE_CTX_free(ctx);
return 0;
}
+
+ if (!EVP_EncodeUpdate(ctx, (unsigned char *)dst + outl, &outl2, src,
+ size)) {
+ EVP_ENCODE_CTX_free(ctx);
+ return 0;
+ }
+ outl += outl2;
EVP_EncodeFinal(ctx, (unsigned char *)dst + outl, &outl2);
+ outl += outl2;
+
+ /* Strip the encoded padding at the front */
+ if (leadz != 3) {
+ memmove(dst, dst + leadz, outl - leadz);
+ dst[outl - leadz] = '\0';
+ }
EVP_ENCODE_CTX_free(ctx);
return 1;